Is there a relationship between family size and attitude toward abortion? It depends on the family. There could be factors that would cause someone to have a large or small family that would also influence the attitudes for abortion. The following is a discussion of some of these issues.
A large family might be less likely to believe in abortion. There are different reasons for this. First, perhaps not all of the children were planned, and if the family would have believed in abortion they would have aborted and had a smaller family. Therefore a family with a larger family might be less likely to believe in abortion because of that. In addition, some families with large families are very religious. Some of them do not even believe in birth control, and they feel that they want to have as many kids as God grants them. Thus if they do not believe in birth control, they are even less likely to believe in abortion. Most people who are very religious are against abortion.
Feelings on abortion are often passed down from parents to children. Therefore if the parents do not believe in it or are very religious, a lot of times the children will feel so as well, and will also be against abortion. Likewise if the family is more open to it, then the children may be as well. Of course, sometimes children purposely do the opposite of their parents if they do not agree with them, so it is certainly possible for the children to feel the opposite way of the parents.
With large families, a child may be used to be around a lot of children. With so many kids around, and being accustomed to it, they may have a more difficult time considering having an abortion. They may be more willing to have more kids, and have difficulty imagining not having one of their kids and thus not going through with a pregnancy, even if it was not planned.
With smaller families, it is possible that the parents had an abortion and this is why they do not have a larger family. Most of the time, however, they have just chosen to have fewer children. Their feelings on abortion could go either way. Again, what might matter more is whether or not the family is religious, and if they are, they may be less likely to believe in abortion.