Not sure about CP & UTI but a great multivitamin (though expensive) that I've been giving my four year old is IntraKID that I buy from Global Healing Center dot com. Our 4 year old is on his 2nd bottle of this stuff (along with 8 drops of 5% Lugols taken daily) and his growth, communication, and demeanor have caused very quick and positive changes that everyone he's been around have remarked on.
I've been giving him Iodine supplements (Lugol's and some Kelp Iodine drops I got from the Vitamin
Shoppe prior to giving him the Lugol's) for four months now; that alone immediately cleared up a nasty sinus infection him and me were suffering from at the time.
From our experience, the more the better. Best wishes.