Softballkid said:
Pontoons a re made to basically just float around at slow paces, in calm waters, they are also used to "party" boats... its not really something you would want to take out in the bay, or put a 40hp motor on, most people dont go over 15hp with them......
Not quite true kid, sorry.
http://www.trackermarine.com/index.cfm?fuseaction=home.suntracker_regency
A Pontoon boat would be ok for the Patuxent but not the bay or the Potomac unless it's a calm day. They are very light and don't need a lot of horsepower to really go. 70 to 100 HP is more than enough for a fun day.
If you're worried about a place for kids to sleep, you can get one like Elaine posted or they come with a bimini top but when it's potty time, you have no privacy.
Pontoons are cheap but a cuddy cabin type is more practical for kids. Go 19' minimum.
P.S. there's nothing to do in the bay so you'll stay in the river anyway.