I can only go by what I have seen first hand with my dad remarrying a woman 10 years younger than him. My brother and I being 30 and 27 at the time and her kids being (I think) 18, 14, 10- somewhere around those ages...it has been really hard for them. His wife went back and forth on wanting help discipling her children and then not liking his ways of doing so. It really seemed they should have thought more of how these things would have been handled prior to getting married and I would encourage you to do so as well. (they have been married 8 years now).
Personally, if it just doesn't come naturally to you to want to be a mother to his children (even more so considering their mother has passed) then I can't imagine why you would even want to date him. There are lots of pluses to how this would work, his children are young and at ages to easily accept you in a motherly role and no exwife to deal with (not to sound cold that she passed, of course).
You really have to decide and set limits for what you want at this time in your life and let that be known up front when you meet someone. You very much have the right to do so. I would say that if this is something you are questioning at all, that in itself really answers the question for you.
Good luck to you.
