If your child is under the proper age and you answer their proper age without getting upset I am sure it will end just fine. When my kids got close to that age (yeah we snuck in that extra trip of them going for free) and we were asked how old, I told them. No problems. If I were worried because my child appeared and acted much older, I'd carry a copy of birth certificate.
Maybe I missed it here and I've never read it elsewhere that someone with a legitimate "free" kid was ever told they didn't believe them after they stated their age.
It's not absurd if Disney feels they have a problem with guests "basically stealing" .... it's why they instituted finger scans on tickets ..... it's one reason they added MB and tied so much to it, to keep the guests from packing rooms with too many people .... it's why they added gates with MB scanners to get in to the pool so that day guests or hoppers don't use .... I will add my week there that to get into parking lots and get my shopping discounts every CM scanned my MB and checked my ID to match.
Innocent people have no reason to get upset.