I would go either up to Baltimore - soooo close! It's great for the 5-7 age range. If you want to drive, go for a ride west to Shenandoah. Go see Luray. Make it a scenic drive. Hell explore all the quaint downtowns of Middleburg/Charlottesville/etc. staying in VA and driving. If you go N to Philly you can drive through MD. Philly is a TON (TON!!!!!!!) of fun.
I would not feel the need to have to drive all the way out of the area. I say this as someone who actually hates the DMV and finds everything around here more than boring. However, I don't have 5-7 age kids, I have teens so we do NYC/Philly. When I'm low on the budget, I get out of DMV and if it's just driving/exploring I want to do, admittedly there is so much to see on that level around here.