You're new to the boards so, you probably have no idea how loaded that question is. Let's try to be nice, everyone.
I'm not sure whether you're asking if it's possible to do this or if it's morally correct to buy a "just-turned-10" child a "child" ticket.
From a moral standpoint, I wouldn't because I feel it sends the wrong message to my child, who knows just how old she really is. The price difference between an adult ticket and a child's is about $40 or less, depending on the number of days you purchase. I don't feel that's too high of a price to pay for a lesson in honesty. I'll cut corners elsewhere to make up the difference.
But, if you just want to know if the people at the gate will question you regarding her age, the answer is "probably not". I have yet to see a CM stop a family and ask them to provide proof of age for a child that looks anywhere close to the age of 10.