Keeping a mask on a toddler UPDATE

Any tips for me? I thought the mask requirement was above 3 but my son just turned 2 a few days ago and has a physical today and they said he is required to wear a mask to enter the building. She said I MUST keep it on him or we have to leave . Any tips? He literally just turned 2 and at home when I tried it on he won't keep it on.

I told him we were going to play Dr like one of you suggested and he kept it on most of the time! He did really well actually!! Thanks everyone