Like you I have kids, and it really takes a toll, and I definitely see myself aging in the mirror. But I cannot recommend training enough. I started working out regularly three years ago, after a long hiatus due to kids. And I feel stronger and fitter than ever as I approach 40.
The kids still need lots of care (they are 5–9 years old), so finding time and motivation is still a challenge. For me the trick is to do training I really like. That helps so much with motivation. So, find something you like!
What I happen to like is bouldering and hiking. I have a fixed day of the week for bouldering, just after work, and I never miss it, because I know if I start skipping I might fall off my training habit.
Then the rest of the training is motivated by getting better at what I love. I do pull ups to better my climbing etc…
I will fight hard to keep at it through my 40s, because it is such a quality of life improvement. I also attribute the fact that I haven’t been really sick the last few years to my exercise.