My 2 year old is a very picky eater. will this affect his growth?

Unlikely: A natural drop in feeding happens as growth slows from a 14lb/10in/yr in 1st yr to a 5lb/4inch/yr in 2nd. They also drive you crazy with their food selections. I expect todlers to feed well about 4-5 days a month, grazing & picky for the rest. Vitamins are ok if you want but most do well without. I like liquid vits at that age, not the candy vits. Todlers may find & ingest adult look alike meds.