Thanks for your great responses, everyone!
Actually, the kids already often have to make do without me, can cook their own meals and all that, when I work lates. I think it's just stuck in my head that they're still 'little'. Heh. I guess I really have no excuse.
And it probably would get them interested if they saw me going and getting results from it. I know from when I have done gym (yearrrrrrrs ago now) or swimming (more recently but fell out of the habit when the local swimming centre shifted and Id now have to catch public transport rather than just walk to it) I did feel fantastic after, much more energetic, mood lifted and everything.
I think if I do it, I might just start with one session a week because of my 'all or nothing' attitude which I need to relax up on.
It was pretty inspiring to hear that some of you manage it even with kids, work etc. I'm impressed.