In July, we will be flying to Baltimore on Southwest. My oldest will be nearly 5 and right at 40lbs -- can I still put her in her MA on the plane? Also, we will be buying a ticket for the baby, 8 months in July. Does anyone know if Southwest offers discounts for babies?
I fly SWA all the time. Dillipop is right about the discount; it's rarely useful unless you are flying last minute and all the great internet fares are gone.
As for the MA, you can put her in it, but you might run into legroom issues. We started flying with DD#1 in her Marathon when she had just turned three, since she had outgrown her RA by height and almost by weight. (She was 97th percentile or more for both at the time.) But then we started running into problems with her legs. The additional height of the restraint means that the child's legs are that much closer to the seat in front of you, since the seats are angled back. That presents problems about kicking, though that would be better with a nearly 5 y.o. than with a 3 y.o. Also, you cannot use her tray table at all. It's doable, but she may not be that comfortable if she's taller than, say, 43-44 inches. We eventually started using the lap belt only on the plane and carrying on a Safeguard Go for use at the destination. That worked quite well, but then, our daughter was solidly over 40 lbs at the time.
If you do use the seat, carry a copy of the FAA recommendation that children under 40 lbs be properly restrained. I have never once had a Southwest gate agent or flight attendant question my use of a restraint, but you never know. Because of her age, they might give you a hard time, and you don't want to have to check your Marathon if you can help it.