For families of young children on the spectrum, the Discovery Museums in Acton is having Especially for Me! day focusing on children and families dealing with autism on Saturday, 3/23 from 5:30-8:30. You must register in advance (you can do so here) and it is free. They keep things pretty low key and it makes for a fun evening.
The next event will be Saturday, April 27th, and you can register for that date here.