This has been a huge question for us. We have been delaying any trip down partially because of the 2 and older rule. Every 2 year old is a different animal. Just look no further than potty training.
We have a 2 year old that finds it fun to wear a mask for about 5 minutes and then won’t do it anymore. Unfortunately, we will be delaying a trip to WDW until either the mask rule is gone or until she matures enough to wear it for the full day.
Unless you already have masks that you know fit her well, I would recommend trying several different brands to find ones that fit the best (and bring a few different types as backups in case what seemed the best for a trial at home rubs her wrong after full days of use). I’ve found that some masks sold as toddler masks seem to be more geared to the size of an 8 year old than my tiny kiddos! I’ve also been watching several you tube videos w/ my kids of people wearing masks in the parks and pointing it out and talking about it. If she doesn’t like having it on, start by practicing wearing it while doing something fun that may distract from it - playing in the yard, w/ her dolls, watching a show, reading a book, etc. Good luck!
The sizing of the masks is DEFINITELY an issue. My 5 year old is teeny tiny - less than 30 pounds, doesn’t even register on the the percentile growth charts, and all the kids size masks are enormous, except oddly the size small Disney masks. They fit him.
I think that possibly seeing every other person around wearing one will help your 2 yr old comply. Little kids like to imitate others.
These are the masks we found first in child-size and they are the only ones my daughters keep going back to. They wore them at WDW in August (age 3 and 7) without complaint and wear them to school/daycare every day this school year. They appear to be comfortable as the kids never complain about them. And, if handwashed at night they will drip-dry by morning.