Meeting someone and liking this person and clicking is a miracle by itself, incorporating each child you have exponentially complicate how you are going to deal with your date or boyfirend as you are going to have priorities like your family, your kids, hockey night and dance class, and then granny and poopsy than you have your girl friends and you may even have a hobbie or two. When you date a single parent, you are not going to receive the same undivided love, as you would if the person had no kids. That’s because the person with kids already has a commitment towards their children, and has to give them their time, their love, their care, their money, their protection, etc. (If they didn't, they would be a bad parent).
When you date someone with kids, there's less freedom. You can't just take off and go whereever you like; you can’t just make love anytime and anywhere in the house, you can’t just stay up till all hours of the night laughing then sleep in the next day, etc., as can two people with no kids.
Also, kids cost money, just as as everyone else does. That means that a person with no kids, by joining their life with someone who has kids, will end up having to contribute part of their income towards the maintenance of their spouse’s child.
Further, the person with no kids will be thrust into the role of parent (step-parent), whether they planned on it or not.
If you decide to marry a single parent, you aren’t just marrying one person. You’re marrying 2, 3, 4, or however many kids your future spouse has, therefore, you had better love those children, or things will turn out quite badly.
Lastly, the parent without kids will never, ever be the biological parent of their spouse’s kids. That child will always have his/her real, biological parents. When one adopts a child, the child has bio parents, but there is no real contact, or any contact, with them. However, when one marries a person that already has kids, most of the time there is contact between the children and the other bio parent, so one is always the step-parent.