I found that watching a few of kid's performers helped a lot - even if it was to find out what I didn't want to do.
The following may be helpful:
Bill Abbot's - stand up magic for kids. This is IMO brilliant stuff - I love his sense of humour and how he thinks about his effects. There's also a great puppet routine in there that will give you a lot to think about with regards to vent (even though the puppet doesn't speak)
Terry Herbert - I can't remember the name of the dvd, but it gave me some great ideas. Not everyone's cup of tea - but the guy knows how to make kids laugh! His silver sceptre routine is legend - especially as to the kind of humour that really seems to work with kids.
Ken Scott - Making the Birthday Dough - . Actually - this was for me an example of how not to do it. Ken is quite succesful - but I don't really like his show - but that's once again my opinion. That said - there are some nice ideas using music and more of a 'modern' show - compared to Terry Herbert.
5 Minutes with a pocket hankerchief - Quentin Reynolds.
Despite what's been said - I still think this is a good dvd to get hold of. I learnt a lot about routining and it's a great routine. I certainly don't do it the same as he does (actually - I got the dvd and the following day I had a show. I did the routuine word for word. It failed miserably - that'll teach me..) I don't really quite like his style either - but had a good laugh watching the dvd. I don't like Max Maven's style, nor Guy Bavli - but their material is great.
Mark Lewis - although I've never seen him perform, but from what I've heard (from him mainly) you will more than likely learn a great deal - so - if you can get to Canada, hunt him down.
There are a whole lot of kid's magic books that are generally recomended - one name being David Ginn. I have found that his books really haven't done much for me - I have a few. It's probably just me because I've heard others rave about them.
A book that I found really helpful was "Creative Clowning" - can't remember who put it together. That was useful in working out my character when I perform for kids. Might not be everyone's cup of tea - and I'm moving more away from a clown type of feel - but you might want to give it a read.
As for what makes kids laugh:
"Look - don't see" - where the kids all see something but you don't notice it, or it hides away as you look.
Things breaking - I have a sign that always falls off the box my props are in. I eventually get the birthday kid to help me hammer it in with this huge hammer and two really big nails. As they nail the one nail in, the other comes out etc.
Doing stupid things and not noticing you've done it - like putting a bowler hat on upside down, pushing a hankerchief into your pocket, but pulling it out slightly every time you remove your hand..
Getting hurt - yep, most kids are a bunch of sadists

- so if you're stretching a balloon - let it snap back and you hurt your fingers etc.
Repitition - applies to all of the above.
I could go on - but I need to get back to my day job..