How old are you now and how old is your second child? I have two kids also, ages almost 7 and almost 1 1/2. I'm over 30 and do notice changes in how my body reacts to what I do, if your second baby is like mine then sleep issues could be huge. My son often wakes at night and I have to go through a day having had as little as 3 hours sleep, working, housework, looking after the kids, being a wife, and finding time to workout. Takes its toll! Women without kids wont understand these challenges and they are very real. Make sure you eat nutrient dense food and more than 1200 calories. You need the energy for your babies and yourself!!
Don't be too hard on yourself, the body does change after children and we have to accept that. You can still look great and do awesome things, make sure your workouts are intense and that way you justify your nutrient rich food. Good luck.