Cutting Trip Short for Son's Well-Being

AITA for cutting the trip with my wife short after I learned that my son's step-grandparents

weren't feeding him properly? My wife and I got married months ago. We didn't get a

chance to go on a honeymoon, but then I planned a trip for us as a couple.

I originally was planning on leaving my 9yo son with his regular babysitter. However,

my wife insisted that we leave him with her parents. I agreed but was hasitant because

my son has dietry ristrictions due to medical problems and my inlaws commented on his eating habits

as "spoiled". I sent him there and gave them a lost of what food he should be fed.

The 4th day of the trip, he video called me and told me he'd been eating only