I'm a single mom of 2 girls. I love it when a guy already has kids. I unfortunately had to have a hysterectomy so I can't have any more but I love children and I usually run when they don't have any because they might want some and leave me later on. I actually am more likely to date someone that has kids, they understand that my kids are the priority until they are grown. That doesn't mean that the man in my life would not be important or special.
I wouldn't run because what if they are fine with not having more kids. Two may suit them just fine. Then again, if a man is going to leave you for that, let him walk away. You don't deserve that kind of man. Besides, have that talk. You might be pleasantly surprised and start a romance that you deserve. I don't have kids and don't want any. My point is that even a woman without kids, like a man without kids, does not mean he/she cannot understand that your children are important, special, and always your top priority. Open your mind :)