Sounds normal to me. Our daughter could be like this at this age. She would also want to pick up and throw away trash.
She was a very early talker and really understood what we were telling her, so we told her, "Yes, trash, yucky, we do not touch."
Or "yucky germs, we do not touch.."
"The trash man will pick up that trash.. "
and then attempt to distract her.
She also started to notice hot things..
She would warn people when she saw a stove, "Hot, no touch!"
EVERY stove, BBQ pit, Candle.. etc.. She would want to blow out the candles on every table at a restaurant.. So we would allow her to blow out the candle on our table.
She would get onto these obsessions.. and we just went along.
So I do not think it is a bog deal, I just think they are very observant, want to help and your son will probably grow up to be like our daughter..
She loves rules.
She follows all of the rules and it almost pains her to bend a rule unless we give her permission.. We call her grandma.. It has served her well. As long as she knows the proper behaviors, expectations and rules.. she is set to go..