Hi Prairie---Going to a gym, or working out regularly, has benefits far beyond weight management. What is most important right now is for you to decide on how you want to prioritize and schedule your day and money.
Exercise ranks right up there with diet, sleep, water and stress reduction as one of the components of optimal health. Running after kids, cleaning the house and mowing the lawn are all great activities and use calories that might help with weight. But this sort of activity does not challenge the muscles or the cardiovascular system. Challenging the body is what makes it stronger and more resilient, especially as we age. You know, the old saying, use it or lose it, is very appropriate here. There are so many benefits to 'working out' that I can't list them here.
Your membership could be considered part of your health insurance plan, as you are investing in your health. I also feel, that for me, if I don't leave the house to work out, I tend to let other things distract me and I don't get my work out done. It also sets a good example for your kids in encouraging fitness type activities for them as well. Help them to develop this positive life-long habit.
I encourage you to consider scheduling your work out sessions and continue, at least until your current membership runs out. At that time you can reevaluate. I know life is crazy with little ones, but sometimes that 'mommy' time alone can be a godsend. Good luck with whatever you do. In health, D.