I can't believe the responses on here! I don't think it's selfish to want to take an opportunity to do something you've always wanted to do. If DH asked me if he could do this and I knew it was a lifelong dream, I'd fully support it and I'd expect the same from him. We all only live once, and if you didn't have the opportunity when you were younger but have the opportunity now, then why not? Your children are old enough to understand. In the grand scheme of life I honestly don't think 9 weeks is a long time. It's a one off, once in a lifetime thing. Yes, your DH and kids could go with you - but they won't share the same interests by the sounds of it or want to see the same places / may not be compatible with the activities you have in mind and you won't get the experience you hoped for and they might not enjoy it anyway.
I guess the things you'd need to consider would be everyone would need to be on board, as it affects everyone. Are the children ok with you going? How much extra would DH be doing - do you usually do activity drop offs or school runs etc, how do you normally split the household running, meals, chores etc? Do you have family support or can you fund some help if needed while you're away?
I'm in the lucky position that DH and I share everything and he takes on his equal share, so me not being here for a period of time isn't a massive issue for him because he's fully capable of looking after the DC and seeing to everything else that's needed. We have given each other a weeks holiday with friends each in the last year - me a girls holiday and him a lads holiday. Could you reciprocate and facilititate a similar "break" or support him with something he would like to do when the opportunity comes?
I think if you feel like you're abandoning your children then you won't be able to enjoy yourself so you need to answer all these questions first and talk it through as a family. Of course it's a selfish thing - it's YOUR dream. But that doesn't mean you shouldn't do it if it's not going to negatively affect others?
If it doesn't feel right though, then the compromise is waiting until the kids are older, or taking all of them with you (if financially possible), or shortening the duration and doing it in 2 or 3 stints instead of one big one?