I would say: look after yourself. Financially, mentally, physically and emotionally. It doesn't harm children to have a mother who takes care of herself. (I was neurotically obsessed by putting DC first and the expense of my own health and wellbeing. I look back and think, how stupid and pointless.)
So: sort out your finances, savings, pension, mortgage etc. Ask for a raise, switch employers/roles to get on a higher income regularly until you hit the top of your salary scale. Or if self-employed, raise your rates until the amount you earn means you never feel overworked and under-appreciated.
Get fit and stay fit. Make sure you do challenging exercise 3-4 times a week minimum.
Speak out. If you are unhappy with how you are treated by family, partner or colleagues address it. It doesn't need to be a drama, but don't let things turn bitter.
There are loads of things I got right in my 40s though: do work you love and find a way to get well paid for it. Enjoy time with your DC - really have fun as a family. Go on outings, play with them, read to them, get muddy with them, teach them to cook and swim and build dens. It's such fun if you throw yourself into it. And make a bucket list then do something from it at least once a month. It's a recipe for happiness.