YANBU to consider it, it's a good idea to think about it now and try to time it so it works best for everyone.
I'd say in terms of kids you would be best looking at now, or waiting until they're college age, which is a long time away. So depending upon the age of your parents it depends if you can wait that long or not. I moved a lot when I was younger, but settled when I was around 10 or 11, and most of my friends are from around that age, so I think in terms of your kids it would be fine to do it now.
Your husband isn't keen, but he isn't against, he probably realises it's something you'll have to do eventually anyway. It's one of those things about marrying someone from out of area, it's bound to happen at some point, so I think he's being sensible.
Logistics would be the thing to think about - where you would go, how you would afford it, where you would work, where the kids would do to school. Things are easier with a plan in place so I would concentrate on that first.
Also bear in mind - 3 hours is a bit too far to be caring daily for elderly parents; but it isn't that far in terms of young people branching out in the world, like you did yourself, so you won't be stifling your kids' futures. And you and your needs are as important as anyone else's in your family, and although they may not be keen on moving, you sound like you may be devastated if you don't, and your parents may end up in desperate need without you, so I would think that is a priority consideration under the circumstances.
You sound like a great daughter to have, your parents are very lucky.