no worries. my advice is to buy everything in DR. pampers by a bag - sold individually are often not so clean and hygienic. not that they go over something very clean and hygienic, mind you
formulas, both liquid and powder are easily available in small and big cans (about 350 and 900 grams).
use only bottled water for making a formula, people swear by agua orbis (also in all pharmacies, shops and colmados, about 80 pesos per galon).
all medicine for kids (just in case) is available over the counter - syrups, supositorios, drops, you name it.
whatever you do not use can be given away upon departure, i am sure it will be appreciated. even one pampers and little leftover formula...