Bethesda?
Let's see, there's plenty of kid friendly places there:
* Mia's Pizzeria and Pizzeria Da Marco are both great and kid friendly
* BGR Burger Joint makes delicious burgers
* Cava Grill (Mediterranean Chipotle-type concept)
* Assaggi (Nice Italian)
* Nando's Peri-Peri (Roast Chicken)
* Jaleo (Tapas - which is nice for lunch, but pretty expensive for dinner)

* Dolcezza Gelato (Fantastic Gelato/Ice Cream)
* Georgetown Cupcake (They have a store right in Bethesda)

A drive south into Chevy Chase, MD you'll find:
* Pete's Apizza (New Haven Style pizza joint)
* 2 Amys (Easily the best pizzeria in the Metro DC Area) A bit of a wait sometimes, but well worth it.
* Le chat noir (French Bistro)

Hi, me and a large group of friends and our kids (8 adults + 6 kids) will be in Baltimore for an event in the B+O Rail Museum.
What's a good and cheap option for lunch with such a large group with kids?
We would like to keep it in the Harbor/Fells Point or thereabouts.

Thanks,

Acacia is OK. And that's the problem. They're not as great as other places in Frederick, and they are pretty uneven: on some days food is good, real good, some day it isn't good at all.
I've had to send steak back a couple of times because they don't get the concept of medium rare.
If you go, stick to fish: they seem to do better with fish and seafood in general than steak/pork/fowl.
There are much better places to have a meal in Frederick in the same price range, most notably The Tasting Room, Firestone's and the excellent Volt which is run by Bryan Voltaggio from Top Chef: Las Vegas.