Well, here's my $.02...I also live in the Philly area (35 mi NW of the city)....I recommend stopping in SC...it's not 1/2 way, but lots more to do. I've been to South of the Border, and I'm in agreement....it is not for me!
When we drive to WDW, we stop at my parents in Mt. Pleasant, SC for a few days (just outside Charleston), go to WDW for 5-7 days, drive back to my parents for 1-2 nights, then head home. Yes, it's a long drive to Philly from Charleston, SC (about 11 hours), but it's not horrendous--we always do it in 1 day. And we've done it on July 4th weekend. My DDs are now 9 & 6, so pretty close in ages to yours, and we've been doing the SC-PA drive for 4 years, so they were 5 & 2 when we started. Charleston has some decent hotels, and if you are willing to go further out from the historic district in the city, you can probably get a pretty good deal, but still be close enough to attractions.
If you change your mind about being somewhere near attractions and would like to get further north on your first day, I would consider Fayetteville, NC (military base there, so lots of hotels) or Richmond, VA area...Or Myrtle Beach? Never been to Myrtle Beach, but I hear great things!
When we drive to WDW, we stop at my parents in Mt. Pleasant, SC for a few days (just outside Charleston), go to WDW for 5-7 days, drive back to my parents for 1-2 nights, then head home. Yes, it's a long drive to Philly from Charleston, SC (about 11 hours), but it's not horrendous--we always do it in 1 day. And we've done it on July 4th weekend. My DDs are now 9 & 6, so pretty close in ages to yours, and we've been doing the SC-PA drive for 4 years, so they were 5 & 2 when we started. Charleston has some decent hotels, and if you are willing to go further out from the historic district in the city, you can probably get a pretty good deal, but still be close enough to attractions.
If you change your mind about being somewhere near attractions and would like to get further north on your first day, I would consider Fayetteville, NC (military base there, so lots of hotels) or Richmond, VA area...Or Myrtle Beach? Never been to Myrtle Beach, but I hear great things!