My friend lives in a US state where her two year old has to wear a mask all day in daycare, and at all public playgrounds.
I was quite shocked when I heard that tbh. I think its too much, at that age children are learning emotional regulation and how to play and share, not being able to see each other's faces is a huge issue.
I also think evidence suggests two year olds don't transmit as much due to their smaller lungs. My own 2 year old was exposed to another toddler in childcare who was COVID-positive, they are best buddies so I'm sure were licking each other all day but nobody in their bubble tested positive.
I think a flight is one thing, as has been pointed out its optional, but I do think the lower limit on mask wearing in the states is problematic.