mothers day brunch, with baby
Chinatown would be my suggestion. When our son was a baby, ethnic restaurants were far more tolerant and happy to see a baby coming in the door than a typical restaurant. Plus, this is a busy restaurant day. There are plenty of suggestions on the board for dim sum, shabu shabu, and others. You could also just go to a bakery and get several different savories and treats and eat there or take your goodies to the Public Garden, find a nice bench, and enjoy the weather (which I am hoping will be nice).