3 year old question!!

I’m not sure if this has happened to anyone else but my step son is 3 years old, going to be 4, recently just started having a weird thing.

Today he’s been getting erect, with his face flushed (red cheeks) and breathing like if he had just gotten done playing. It’s happened about 3 times now. Is this something ‪I️‬ should be concerned about or is this just his body doing weird things as he ages? He is not complaining of any pain but he is noticing it as well.