There's a lot that goes into planning a party, but planning a party for kids requires more work because their attention spans last about 5 seconds. That's why it's important to be creative with the activities and make sure you actually plan out what to do. At a more grown-up party, you just let people mingle but kids don't have fun like that, it's your job to create the fun! 

My parents usually did our birthday parties at home. That meant they planned pretty much every second out so that there would be minimal time for kids to be bored and complain. There are always classic things like the piñata that never die and can be played forever, and when the kids are younger, it takes them a LONG TIME to get that thing open!

I have the advantage of having a summer birthday which meant we had my entire birthday outside. We played games that involved water balloons and a key aspect in children's birthday parties is that there has to be a prize for the winning team/person. Whichever team throws their water balloon back and fourth without breaking it the longest gets a prize. A game we always had was one in which one person from each team sat at one end with a galloon (like from milk) on their heads and each team had a bucket of water at each end and the object of the game was to fill your gallon up first (you used a small cup). The person holding the gallon on their head always got soaked because people were racing and let's face it, kids are still developing their motor skills and can't quite pour perfectly, especially under pressure. 

With kids I think it's important to make a big deal about the cake and party hats and things like that. I had a friend from Norway who was here for a year so we through her an American style birthday because she had never had a birthday cake before. Nobody had ever sang "Happy Birthday" to her and made her laugh or blush while they sang. Nobody had ever made her wear goofy hats. So of course, as she experienced American culture, we as her friends, felt it was our duty to introduce the big deal of the birthday cake to her and she loved it. It makes eating the cake and opening presents a lot more fun when you've got party favors and silly hats.

Finally, it never hurts to come up with a tradition. My tradition was that every year my parents would make us do a pyramid. I have a photo album in which there are pyramids of children, most of them stay the same but they get older and it's really fun. Everybody always knew that it was part of having a birthday party at my house, you had to do the human pyramid. We pretended we were annoyed by it but we all loved it and now we are able to look back on those pictures and we are SO glad our parents made us do it.