Keeping kids entertained can be a full time job. If you're taking care of somebody else's kids and don't know their interests, this tutorial might give you some ideas to make the time enjoyable for both of you.

[edit] Steps

Ask them what they want to do first. There's no need forcing an activity on a child that already has their mind set on something.
When children don't know what they want to do, ask them to show you their toys. Maybe together you can find something fun to do.
Having a child pick up each toy and tell you a little about it might speed up the process of finding the right toy to play with. And even if it doesn't, it will at least occupy some time and keep the child from being bored. You might find that the child will want you to play too, but don't be offended or surprised if they find the toy they need and forget you're there entirely.
Make sure to clean up!! No parent likes to come home to a mess. Make a game out of picking up the toys at bedtime.
Remember the image you project; this is a job and the parents are your employers. Wear clothing that is modest, clean, and appropriate for the activities you will be doing with the children.
toddlers especially like things that they can destroy, like build something out of soft blocks and let them destroy it, you'll keep their attention for hours doing that.

[edit] Games

Set rules before you play a game. If you're playing outside, make sure that all the children stick to the backyard and as far away from all streets as possible. If you're playing inside, make sure that all of the children stay inside and that they stay out of all off-limits rooms, such as their parent's room. If you're playing with a child younger than four, stay with that child while you're playing a game, and be aware of where the child is the entire time you're babysitting.
Have them make a skit for you to watch. This is a good thing to get them to plan while you prepare lunch, or change a baby's diaper, or put a little one to bed. They really enjoy it! (Even if it's extremely boring, look like you're having fun! Most of the time, though, the kids come up with some great ones.) Before you leave the kids alone, make it clear that they can only stick to a certain area (like the playroom or a bedroom) so that they aren't looking for prop ideas in other rooms and that should prevent the children from getting into mischief.
Play Freeze Dance! Take turns being the person in charge of the music, and turn it on and off. When it's off, stop. When it comes back on, dance! You can also play this just moving, if you don't want to dance.
Pick one person to be "It". Everyone else moves around (dancing, jumping, or just walking) and when "It" says "Statues!" everyone freezes in whatever position they were in (if someone's arm is up, it stays up, or if someone's in a running position, they stay in that position). "It" walks around trying to make one person after another laugh. Whoever laughs first is "It" next!
Play sardines. Sardines is the opposite of hide-and-go-seek. "It" hides in a space big enough all the children playing to hide, while the rest of the children count. When everyone is finished counting they all look for "It". When someone finds "It", they join him/her in hiding. The last person who finds "It" is "It" next! "It" or not, they'll have fun!
- If you're playing with a child 4 years old or younger, always have the child with you. If you or the child is "It", have the child hide with you. When you're looking for "It", look with the young child.
Play the snail game. Using the chalk, make a snail shape on the ground like the one to the right (the snail head is optional). Give each player a different color piece of chalk. The first player takes the stick or small rock and throws it onto a square of the snail. That player then walks on all of the squares of the snail starting at the snail's head and going around until they get into the middle of the snail's body, but the player jumps over the square with the stick/rock on it. If the player steps on all of the squares without losing her balance and without stepping on a line, she gets to write the first letter of her name in any one of the squares that she chooses. Then its the next player's turn, only now that player has to skip the square with the rock/stick in it and also the square with the first player's initial in it. Every time a player gets around the entire snail without stepping on the square with the stick in it, without stepping on a line, and without stepping in squares with their opponent's initials, they get to pick a square to put their initial in. Players are allowed to step in squares that have their initial, but not in squares that have an opponent's initial. The game continues until all of the squares are filled up. The player with the most amount of squares filled with her initial wins.
- Place: Outside, on a driveway (or some open place where the chalk you use can be washed away by the rain. Not on a covered porch or similar place.)
- To make the game a bit easier, change the rules so a person can write their first initial in a square if they make it around the snail without losing their balance and without stepping on a square with an opponent's initial. This is instead of without losing their balance, without stepping on a square with an opponent's initial, AND without stepping on a line.
Create a menu for an ice cream shop shop. Make one on your computer or just hand write one. Make fake money and give an equal amount to each child. When you play the game, ask the children what kind of ice cream they want, how many scoops, etc. Then take turns being the Ice Cream Man!
Have one child go to the pillow or chair in the center of the room to play the "Daddy" and close their eyes. Everyone else goes to the center of the room and everyone say together "Don't wake Daddy!" After they shout all the players walk around "Daddy" in a circle not making a noise. When "Daddy" hears someone make a noise, he/she says "Bring bring bring" then he/she counts to 5 out loud. When "Daddy" starts saying "bring bring bring", the other children all run to their pillows around the room and pretend to be asleep. Once the "Daddy" is done counting to 5 he/she opens their eyes to see if anyone is still running to a pillow or not looking like they are asleep. If someone is not doing what he or she should be doing ("sleeping" on a pillow) then the "Daddy" calls their name and they are the new "Daddy".

[edit] Tips

If you are babysitting at night and the kids are smart enough they'll try to stay up later then their bedtime with "I need some water," "I need to use the potty" or "Read me a story." Get them in bed a half hour early, that way, if they try to pull this nonsense by the time they're done it'll be their REAL bedtime, chances are, they MIGHT NOT even pull it, they might be tired and the parents will be satisfied that you got them to go to bed so early.
You'll get further with a kind word and some crayons than you will with just a kind word.
If the weather is nice and there's a safe, enclosed area outdoors, and if it's okay with the parents, let the child run around outside. Just remember that outside play requires constant supervision.
Try and have fun with the children. Chances are, they'll have fun too!
Any good babysitter knows that if you're babysitting in the evening a bedtime story is the bee's knees. Bring your own book or you might visit the library and pick up a few good stories.
Let them do what they want to do, even if its playing star wars. And play with them.
Sock wars are a good choice for kids 4 and up. You get socks, then hide from each other and throw the socks at each other. It's a blast.
Incorporate picture books into your babysitting experience. Children often have favorite books sitting right on their bookshelf. Ask the child to show you some good ones and then cuddle up together and have a good read. It is also helpful to bring your own books to insert a little variety into the child's reading routine. You might bring some childhood favorites with which you have been unable to part, or you might visit the library and pick up a few good stories.
Pretend they are your siblings. Little kids love to be tickled.

[edit] Warnings

Watch out for small objects if you are babysitting young children.
Never leave a baby or toddler unattended.
If you are playing sock wars make sure there isn't stuff that could easily be knocked down and broken. The kid's parents won't be too happy.
Never punish a child by hitting them. It's best not to punish them at all as you are just there to have fun, but if the kid(s) are really acting up, a time out for 5-10 minutes will suffice. Any longer and they will absolutely hate you.
If a kid is scared of doing something or doesn't like that game or food, don't make them do it, play it or eat it. They have their reasons.
If you are a young lady make sure that the kids father doesn't try anything. If he does, tell an adult, whether it be his wife or your mom and don't babysit for them again.
If the parents come home in a condition in which they are unable to care for a child, don't leave them alone with the kids. Call your parents so they can come help you and never let them drive you home if you think they've been drinking.