Related to the popular slang term: wheels.
However instead of "wheeling" (seducing or trying to get with) people your own age, or people around your age. Training wheels is aimed for people who have a nasty habit of flirting with younger guys/girls.
Training wheels: to wheel people that are way to young for you.
Training wheels: someone who has an uncanny ability to befriend little children.
A: Whoa, Jessica has some crazy training wheels!
B: I know right? Those kids are basically her slaves!
A: Goddamn, I wish I had those kinda wheels.