OK, so it sounds like you have a 3 yo and a 2 yo... First of all, I wouldn't bring the carseat. Do everything you possibly can to avoid that hassle. I have traveled from the east coast to the west coast and back both ways and I emphatically recommend leaving the carseats home. If you are renting a car at your destination, you can usually rent a carseat as well. If you are not... I assume you're visiting family... try to borrow one from a friend or family member while you're there. I've done both. It is really worth the effort when you don't have to struggle with two carseats, two toddlers, a bag of snacks and goodies, and the airport crowds and lines.
If renting or borrowing is not an option, check those carseats and let the children have room in their seats to wiggle. My boys are 6 and 3 right now and the last time we traveled that far was a couple of years ago... there was no rule that they had to have their carseat on the airplane... and they really enjoyed the freedom of movement (right in their seat!) during the flight.
As far as the stroller... if your little ones will hang out in the stroller during the wait, great... check it at the gate. I also found that letting them get a little energy out before the flight was helpful, so we would play games with cars in a less populated waiting area, or try to walk on only one color of the patterned floor, take a walk around the terminal... that sort of thing. Nothing crazy... no running...
Also: when you pack your carryon... try to use backpack styles. Even the toddlers can carry their own backpacks with their own crayons and goodies... not very expensive at Target to get a fun design small backpack and they feel great because they have something new and exciting. If they get sick of carrying it, hang it from the stroller. Most important is your backpack... I found carrying a shoulder strap and constantly bending over to attend to the children was a real pain. Make it easy on yourself.
Hope this helps. Have a great trip. Remember: 3 hours isn't really that long. You'll be fine.