It's an intriguing question, but in the end there are only three possibilities: the mother, the child or both. The 2nd option can pretty much be discarded completely as it has been explained that one bite is enough to gain the power of a DF and that you can throw the rest away. So it's kinda nonsensical that when the mother takes one bite, it goes to her stomach and that the powers soon should be active, somehow the child would have gotten preference over the mother. It makes no sense, so it's pretty much a given that the mother will be affected by the DF.
Now that then still leaves the matter of whether it's only the mother or also the child. If for example she would have the power of a logia and someone tries to injure her belly, well normally a logia would just let it pass through and regenerate, but what happens then to the child? Though this can be solved by stating that as long as the child is still connected to the mother, the DF affects it. However from the moment the child is born and gets disconnected, that influence is over as I think there is little doubt that if someone asks Oda this, he's going to answer that mother will have the powers of the DF.