I'm in the same boat, and to be completely honest, I would have never had kids if I had known I would develop PTSD. I know that is terrible to say, but I really feel guilty for not being able to meet their needs.
In my case, I am lucky in that my husband's family is very involved in my children's lives, which I feel, covers some gaps where I fall short. I keep trying to tell myself that I need to get through this stuff now, so that I can be there for them later. And that, when they see me in therapy and doing all of this to heal myself, that it hopefully sends a strong lesson to take care of their own mental health/ engage in self-care/ and to reach out for help if something ever happens to where they need it.
I also hope that one day, when they are much older, I can tell them my story and maybe it will help them understand why things are the way they are.
I don't have any easy answers. I've found that cutting back hours at work, even though it causes financial strain has made a huge difference at home. Putting my youngest in full-time daycare has also helped. (It might work to hire a sitter a few hours and take that time for quiet--esp. if you can get the sitter to take the kids out). This way, I can take those hours when my children are at school to engage in self-care. Another lesson learned the hard way, is to just stop when I get really stressed or my anxiety ramps up. Instead of pushing through all of the household chores, a nice dinner, etc. it's just better to go to my room (once I have the kids distracted by something else) and just calm myself.
It's a learning process, and one filled with guilt, tbh because I'm not the parent I want to be. But I try really hard to tell myself that I'm doing the absolute best I can in the situation, and beating myself won't help the situation. I wish I had more things to say on how to help the situation, but I don't think there are easy answers. Mine are 8,6, and 3. It's easier as they get a little older, are more self-sufficient, and don't always need constant supervision, but it is still difficult.