Supplementing?

My little one is very picky when it comes to whole milk, absolutely will not take it. I sneak it into his meals tho so he gets at least some. At our last doctors appointment our pediatrician mentioned he was falling behind on the growth scale. I’m starting to consider Pediasure. Probably 3 or 4 drinks throughout the week? He’s a great eater with a fast little metabolism but something isn’t working out for us.😕 Any other moms supplementing or have in the past? Help a girl out with some advice.

Update*

Spoke to our pediatrician about my concerns, he told me as long as he’s eating pretty good and getting a variety of his food groups to not worry about pushing whole milk. Lil dude will get what he needs. Thanks for the comments guys!