I found that the PICU is a very Med-Peds related subspecialty. Many people who trained Med-Peds go to the PICU. Probably because of the ICU time they have to do for training, also probably due to the broad range of ages they see there. When I did my sub-I in the PICU, 3 out of 4 the attendings were med-peds as well as the fellow.
I'd also recommend doing a med-peds clinic elective (possibly as an audition rotation). University of Rochester has an excellent elective that is open to visiting students.