Where I live (Toronto) children 2 and up need to wear a mask in indoor public spaces, including shops, doctor’s offices, hospitals, buses, and community centres. My DS is now 2.5 and wears a mask with very little trouble for about half an hour at a time. Longer than that, he starts pulling at it and toying with it. But for short errands, he’s 100% fine and it’s a total non issue. DD4 also has to wear a mask in school all day long and has less trouble with it than I do!
It helps when all the other kids are wearing them too.