Here's a start: These are the U6 to U12's rules.
http://www.rugby.com.au/tryrugby/KidsRugby/KidsPathway.aspx
You should be able find more links from there.
We had an interesting experience this year when we were scheduled to play a touring u11s team. In NZ, u11's play a full 15 man team, full field rules but uncontested scrums. Our u11's rules are 12 man teams with side-lines marked 5m in on each side but with contested scrums.
The NZ team pretty much demanded to play by their rules and were told that our u11's team would not be allowed to play due to ARU rules and for insurance reasons (although we were happy to accept the non-contested scrum). The kiwis refused to budge and went on only to play u12's teams. They got smashed in their first game against the u12's Helensvale Hogs. Not sure how they went for the remainder of the season.
So basically; u10's and 11's have 6 man scrums and can not push further than 1m. Also, No.8 moves from the back of the scrum are NOT allowed.
NZ rules are 8 man scrums but uncontested - not sure about their No.8 moves.