Family looking for tasty dinner near Commons
A little more specificity would be nice -- I think Penang is a good suggestion, but there are a lot of places in the area that could meet the criteria.
Are you looking for tablecloths or no frills?
Some of my other favorites in Chinatown include New Jumbo Seafood (Hudson St. -- lots of fish swimming in tanks that if you order you see them grab with a net, could either be cool for tweens or horrifying) and the original (?) Pho Pasteur on Washington St.
One of my new favorite places in the area is Marliave -- it's definitely cool, the food is fantastic and I like the cocktails, but it might be a little tough with a toddler and will be a bit pricey.
If you're looking for solid, cheap, basic food in a nice setting that's family friendly I'd even risk foodie scorn by going to Maggiano's (on Columbus next to the Park Plaza hotel). It's not fancy and it's not the North End, but the portions are cheap and ENORMOUS and I've never had a "bad" meal there. Not everyone's cup of tea, but especially for a toddler I think it could make sense.
I'll second Marliave, and it's not as pricey as all that. They have plenty of great dishes at around $10, like burgers and house-made pastrami, as well as more elaborate food for the grownups (not that a grownup can't appreciate a great burger!)
It's also historic, having been a restaurant (under various management) since 1885. It was even reportedly a speakeasy during Prohibition. http://www.marliave.com/home/
They're just over a block from the Park St. T station.
10 Bosworth Street, Boston, MA 02108