Shaving baby’s hair

Hi. Is it a must to shave baby’s head at least once? My in-laws have been nagging to shave it since birth. My son is 15m now, and they still wont let go. They keep telling me shaving is good for the baby. The hair will be even and thicker. Tbh, that doesnt matters to me. And so they changed their statement now. Now they tell me my son cant go into the temple if he doesnt shave. I told them me and my siblings did not shave as well. Why do they insist on shaving it?