If they are going inside, then they are happy to try -- but it's not a big chance that they'll have a baby even if they do go inside. It might take more than 20 trips to the hut (they go indoors even if they are not successful making a baby).

If you really want to speed this up, you can interrupt them -- they do not need to go indoors for the breeding to be successful. Just pick up the female and drop her on the male again to repeat the try -- if your population increases when they kiss, you have a baby. If not, pick up and try again.

383 is apparently enough food if they are trying to breed on their own -- 400 is a rough estimate.