I'd rather not. I've done that in the past. It is a very tricky circumstance. You have to realize you're walking into a pre-made family, and just as if you had kids too, you have to realize you don't have the same freedom and time to spend together you would if there were no kids. It can be somewhat frustrating to enter a relationship and already have the restrictions of children. And then you also have to consider what if the kids don't like you. Then there is the mothers battle over her wanting/needing a man in her life, and considering her children's happiness.
That being said, it's not to say it can't work. It can, and does, work out. But it is definately a trickier prospect.
Though, for me personally, at this point in my life, i'd rather not date anyone with kids. I'm 37 and spent a lot of my life in depression, or illness. I just want to enjoy marriage, and have freedom of the financial and time constraints of children and try to enjoy the last bit of my life with someone. Perhaps if the kids were teens and able to be more independent, and have lives of their own, instead of younger kids, i might consider that. I don't know. I have my preferences, but, in the unlikely event, i find anyone, who knows what i will ultimately decide.