hi yiyi123,
usually by 3 mths, babies are curious and strong enough to grasp at things, esp hanging toys on the playgym, so dats y pple say it's time to remove the mittens.
u myt wanna continue watching him when his mittens are off so dat u can stop him when he's abt to scratch his face. or u can take his mittens off only when it's playtime at the playgym.
but nowadays the weather is so hot, i'm also likely to take off my baby's mittens soon. cos his hands get stinky due to the sweat buildup under the mittens.