I did a google search on "average weight height children" and this is the link I liked most ---
Are these Child Growth Charts superior to others?
If you don't like this one, try doing that google and pick one that is more to your liking
If you're truly worried your child is having growth issues, though, I recommend talking to your doctor - my son's doctor has discussed this with me, and shown me charts, and tells me why he's okay where he's at
(he's very short...I think he'll take after my mom who is only 4'9" hehe)