http://www.usawmembership.com/age_group_weight_chart
Follow the link above to find out what age division your child will be in for the upcoming year and what weight classes USA Wrestling uses at regional and national events. However, always check the individual tournaments information as sometimes they use deviate from USA Wrestling.
For a complete list of USA Wrestling events follow the link below
http://usawevents.sportngin.com/page/show/1019486-regional-and-national-events-schedule