That episode shouldn't be a problem when he's back with his siblings and moving. It's important that he keeps warm, their digestion doesn't work when chilled.
What you can do to give him a chance to catch up is to take 3 or four of the fattest kits out of the nest ( into a towel nest in a high bucket, or so) for one feeding time, so he has less competition at the teats. Normally they feed around dusk and dawn, return the kits when you're sure the doe is done feeding. If the rest is all the same size I would repeat that with 3 other kits 2 meals later. One or two full tummys can really make a huge difference.
The fatter kits can miss one out of 4 meals without any problem.