I echo OBP, but if you're definitely going into pediatrics, you will get NICU time starting intern year and PICU time by second year. The only reason it might be helpful to do a PICU elective is if you think you like critical care and some find they get their PICU rotations a little late to decide second year if that's a fellowship they want to do. But I get the feeling critical care is not your thing...
in that case, if you are going to do peds for sure, I encourage you to do as many other electies as possible-- radiology, anesthesiology, etc.-- broaden your horizons. plenty of peds to come in the future.