Most everyone worries about losing weight after having a bab(ies)y. It might be difficult in the couple months following a birth. Your body needs a chance just to recover from the physical demands of a pregnancy and birth. But once the babies are mobile and begin to eat, the worry should subside. Your activity level increases with their age.
Once the babies start eating (especially on their own) the amount of activity is taken to a whole new level. Despite efforts to be prepared, it is inevitable that you will have to get up at least once to retrieve something. As toddler-hood emerges, this once or twice a meal occurrence multiplies. I now often eat zero calorie meals. I would say in an average meal I am up and down about 5 - 10 times - runnng back and forth to the kitchen - picking up things that have fallen, etc. Of course, there are those days that sitting down is just an illusion. It can be a terrific weight management/exercise program.