Yes, both parks can be done in that time frame.
You're coming at off peak season, which is good. February is my favorite month to visit.
I went on the park web site and the hours are not listed for January 2003 yet, but I bet they close at 6pm, they always open at 9am. So you'll check in, and have a few hours to visit a park. That will give you about 3 hours Friday night, and all of Saturday. Goto USF and do a few attractions. It's a big park, so do a few movie rides, and you'll have an idea of what you want to see the next day when you come back.
Saturday morning, be at the gate of IOA first thing when they open at 9am. It takes about 3 hours to do a lap, going clockwise with light crowds. After that you head over to USF and do more attractions.
Late in the day the teenagers will want to head back to IOA and ride the coasters again.
You'll see alot, but believe me, the teens will be begging you to come back.
And will you let the teenagers go off on their own? The 2 year old will slow you down. I'd suggest you give watches to the teens, and make meeting spots, and let them go off on their own, depending on their age. A 2 year old will be sleeping in a stroller, and the teens will want to run from attraction to attraction. If you could leave the 2 year old at home with grand parents I'd say to do that.