S.B.
I traveled by air just 2 years ago. You can bring empty sippy cups and then buy water, milk whatever after security to fill them. You can check a stroller at the gate and it doesn't count for your baggage. You can rent carseats. When I did it was $50 to rent a toddler carseat from a car rental agency. Are you renting a car? If not, there are some places that will rent carseats (mostly in major cities). I just checked Walmart and you can buy a no frills convertible car seat for less than $50. Can your 4 yr old just use a booster seat? It might be worth the money for your mom to buy a cheap backless booster for the 4 yr old (they have ones for $18 at Walmart). If you don't want to take a stroller, you can rent them at most zoos, malls, etc. They usually aren't too expensive either. Both of your children could carry a backpack on with some toys and snacks. I wouldn't be worried about the plane ride itself. I would see if you and your husband can split up so both kids could have a window seat. That in itself will keep them entertained for awhile.