Maybe because a first trimester fetus isn't a child.
Do you really believe that?
If that's your position, then you have no basis for restricting first trimester abortions for any reason.
But let's take this argument a little futher. Suppose the raped woman, for whatever reason, is unable to get an abortion before the 2nd trimester. Suppose the rapist has her tied up in a cabin in Montana and she can't escape until the 2nd trimester. Would you deny her an abortion then?
During the first trimester (around 2 months) -- clearly lots happening during this time.