you can use the rec facilities on post and workout for free. The daycares on post usually have an hourly babysitting service as well. If you don't want to use their gym then you might want to check out your local community center or ymca as they are usually pretty reasonable and have childcare available while you work out. Get involved in your FSG group and see if any other wives would like to get together and walk a few times a week. When the weather is cold go to the mall or maybe your school would let you walk right after school in their gym or the post gym. Tracks also work well especially with the kids. The older ones can ride their bikes and don't have to worry about street traffic while the wives with babies push the strollers. You will be surprised at how many other military wives in your unit would like to have something to be involved in and get to meet other wives.
I know I was an army wife for 12 years and some FSG groups were good and others weren't so good. I liked to meet other wives and a lot of them would come to my house and play games when the guys were gone and we had a lot of fun and everything we planned we had the kids involved. We would take the kids to McDonalds and visit while the kids were playing, go to the park, have a walk in the mall and stop for a while in the kids area so the kids could play, or go to one of the wives houses (most of the time it was mine) and everyone pitch in potluck style for dinner. No one likes to cook when the husbands are gone because there is a difference in what kids typically like and the adult type foods so we would all decide on a type of food and everyone bring something to go along with it. Tacos work well for this or have a chinese night, mexican night, or an all out potluck variety night. All it takes is getting connected with 1 or 2 wives and then they may have other friends in the company then before you know it you have at least 5-10 wanting to be involved. Those were the fun times and keeps the wives from getting lonely and depressed.
oh and Situps also help with shrinking the belly.