My 3 year old boy

Lashai • I`m 29 years old with 2 children I'm a hard working mom just letting nature take its course
So as my baby boy gets older I've noticed that he likes to sleep or even sit with his hands in his undies!!! Now I've heard that this is normal for boys and also men as well but what shocked me was how early it actually starts for youngsters!!!! Anybody else have been in this case before???