First up: sympathy. I have a toddler, lupus and fibro. The struggle is real.
Sleep is obviously the biggest thing for me, but exercise is the next best (for my particular physical limitations, walking or cautious weight training is ideal). Nutrition doesn't make as much of a difference for me as getting a half hour walk everyday.
Things that help, but less than sleep, walking and nutrition: getting time outdoors every day. Getting the right mix of people time and introvert time (difficult with kids!). Setting good boundaries so I don't get used up emotionally, and being very choosey about who I spend time with. Therapy has been helpful. Being on the right meds (another obvious one! but still needs to be said). Taking iron and vitamin D, because I can't keep my levels up without supplements.
The only thing that has helped me find the energy to do the things that make me feel better has been cutting out other things. I only work part-time, I don't study on top of work, we're spacing our kids to minimise impact on my health and sleep, we have a cleaner, we live close to work and amenities... My whole life is pretty much arranged around enabling self-care. Much easier said than done, particularly for people who get diagnosed after they already have kids. Also, no point trying to do anything but sleep if I'm having a flare-up. When my disease is crushing me I just have to wait it out and then start up again with the fatigue reducing activities when I'm capable (this is also enforced by my medical team - I'm not allowed to do more than 15 minutes of gentle walking a day when I'm badly flared, for example).
Given the time of year, and assuming you're in the northern hemisphere, I wonder if lack of daylight could be contributing?