No limit to the number of programs where you can do "second looks", but why would you want to re-visit more than one or two? A second look might be helpful to clarify questions you might have about a program, and might be viewed as a sign of sincere interest. But don't expect to have the same "red carpet" treatment that you had during your initial interview. If you go on a second look, you should be as flexible and non-demanding as possible. It is good to ask for permission prior to your visit if you want to attend a conference or rounds or if you want to see more of the facilities. Remember that most hospitals have fairly tight security (or should have), so don't assume that you can roam the wards, clinics, etc. unaccompanied. Second-looks in peds are not particularly common and probably aren't expected by the programs.