The Allentown Farmer's Market is open Thurs/Fri/Sat if you'd like to pick up some yummy food. They've got homemade Amish baked goods/deli meats and cheeses, lots of fruits and veggies, butcher shops (beef/pork/chicken/seafood), dessert stands, Dan's BBQ Chicken w/rotisserie chickens, homemade pierogies, chicken pie, etc, plus various other places that sell food. A nice place to stop and pick up food if you didn't get much to eat at DP (or you didn't want to pay the high prices!). It's probably 10 min from DP.
Take Rte 222 (Hamilton Blvd) North towards downtown Allentown. Turn left onto North Ott St (at the traffic light-you'll see a park on the left side of the road). Go a few blocks until the traffic light at Chew St. Turn right onto Chew St, which runs through the middle of Muhlenberg College's campus, and follow it until you get to a cemetary (just after 22nd St). Just after the cemetary, on the left side of the road you will see a parking lot w/a chain link fence around it. The big building in the middle is the Allentown Farmer's Market (the grounds are also used to the "Great" Allentown Fair, hence the fence).
There are two places close to DP that your kids might like. I highly recommend Bounce U, which is right up the road from DP, on Hamilton Blvd (behind the Dunkin Donuts). It's got lots of bounce house/bounce obstacle course (slides, tunnels, climbing walls) things inside. Google Bounce U on the web and you can see what it's like. DS3 LOVES to go there. They have sessions for specific ages though, so I'd jot down the preschool open bounce times for when you'll be there, along with their phone number. It tends to fill up quickly on rainy days, but you can call ahead and reserve spaces. In fact, I'd call and reserve spaces tonight for the time you might be there. They don't require any CC info or anything to reserve spaces. DS is TIRED after the hour and 15 min bounce time

. They don't have food (other than a couple of bags of chips for sale) there, but there is a pizza place a few doors down. Cost is around $6 for kids, parents/adults are free. Just make sure the kids have socks on, because they'll make you buy their's if you don't.
The other place is actually around the back of the same building that Bounce U is in. It's called Jungle Fun. They have slides and tunnel mazes, like you'd find at McDonald's (except a little larger). They also have game machines in the back (whack-a-mole kind of things). I haven't been to JF in a while because it tends to be dirty in there, and I've heard they recently started charging adults admission as well (so basically you're paying them to allow you to watch your own children

).
Heading south on Hamilton Blvd (towards Reading/Trexlertown), a few miles down the road there is a McDonald's w/an indoor playground (next to the Giant grocery store on your left) and another indoor playground at Chik-fil-A (on the right, across from Wally World, in the same plaza as Panera Bread and Walgreen's).
Ice Cream World (across from DP) has yummy ice cream! I hope you have a good time.