Definitely do pediatrics, it's the best
Some of the fields that you describe can probably be a significant part of your practice as a general pediatrician--you're never going to know as much as someone who did a full adolescent or child psych fellowship, but a lot of general pediatricians feel comfortable doing basic things like prescribing OCPs or SSRIs, counseling patients, and then referring for anything that gets over their heads.
Medical genetics is probably outside the scope of general pediatrics. Where I did residency they were working to set up a "complex care" clinic which was staffed by general pediatricians who were comfortable with a higher level of complexity and would take ownership of coordinating their care, so naturally they saw a number of kids with weird chromosomal problems. But I don't know how common those kinds of practices are, or how practical honestly. ID is primarily a consult service and is pretty specialized. Outside of keeping up to date on your community's antibiogram so you know what to prescribe for things like cellulitis, you're unlikely to really do much that's truly ID.
One nugget for thought is that both psych and genetics have combined residency programs where you can consolidate general pediatrics and either psych or genetics into a 4 year residency. So if you find yourself drawn to one of those fields, you're not necessarily locked into a 6 year (3 year residency/3 year fellowship) commitment.
If you're interested in a sub-specialty, chat with the program director or department head for the division at your home institution. They likely can let you know if there's an elective you could take during 4th year to gain exposure to the field, or possibly you could even design one. If research is your thing, there's also undoubtedly some chart review that they've had on the back burner that you might be able to help with.
