I think a 2 year old is old enough to know if they want to uncover themselves BUT some options are right. A blanket sleeper and a very light blanket you can breathe through easily.
BUT!!!!!
One thing every doc we've ever taken kids, from new born up, said that we should dress our kids like we're dressed.
That means if YOU wear a tee shirt and shorts to bed that you should NOT put your kid in sleepers and cover them up with blankets, they should ALSO have on a light weight top and no covers on their legs.
So if it's warm enough for you or cool enough for you then it's the same for the kids.
I can't tell you how many times I've seen mom or dad drop off a kiddo to child care and they're in their normal clothes, no coat or even a jacket or sweater and the kid is basically in a snow suit with gloves, head covered, and warm snugly boots on. The kid gets unwrapped and is covered in sweat. The parents go through the whole day without a coat and are slightly chilly at times but they expect their kid to sit in a vehicle with a heater blasting so they'll be warm enough in several inches of coat.
Don't do that. If your house is cold at night then you need to figure out how to make that child's room a bit warmer and a space heater isn't it. If it's 74 in your house don't put your child in a blanket sleeper because they'll be up all night crying from being too hot.
Think this through. Put yourself in this child's place. Are they cold? Is there a light that shines in their face? Do they want something over their face to feel comfortable? What is the reason? Then figure out what their environment is. Is it too cool in the room? But okay elsewhere? Too warm in their room but cool elsewhere?
I never understand why parents have the house cold because the heater is next to their room and it gets too hot if it's on very high. I shut my vents so that the rest of the house can be comfortable.
I like to sleep where I am comfortable. I don't like to be hot and I don't want it to be too cold if I need to get up to go to the bathroom. I keep a small space heater going in the bathroom, a ceramic one, that is pointed at the toilet. That way I can sit down and not get a huge shock. Our room is about the furthest room from the heater and our windows face the north too. So I have to be careful to not heat up the rest of the house.
My point is this, figure out why he wants his face covered if you can and try to fix that. IF it's just a comfort thing then get him the thinnest, sheerest, blanket you can find and see if he will use that. Then he should be dressed for comfort the rest of the way. If it's hot in the house he needs to be dressed for hot temps and if it's cold inside, inside, inside, then he can be dressed the same as you. IF it's not warmer in his room than yours.