Panting could be sign of trouble: heat stroke or respiratory distress,
possibly related to the trauma of separation, delayed nursing etc.  I
would call my vet, make sure the nest has cooling and moisture -- like,
perhaps a damp cotton dishtowel?  Something light weight and not too
cool to shock the kittens.  Water? condensed milk?

You still got the Mom cat?... Run her back in there. She probably had
hard labor you know...and is just looking for a break.

If they are still in the drawer, maybe you can relocate them to a warm
dry dim place...big enough where mom can layout while they feast.

Can you get them to a vet?  They may have been away from their momma for too
long when she couldn't get to them.  If you can't get to a vet right now,
get some KMR (kitten milk replacer, available at Petsmart type places) and
try to get some formula into them.
Please get them to the vet first thing in the morning.  They may be
dehydrated.

Perfectly normal behavior for active kittens if it doesn't happen too often.
Like dogs, cats can pant to cool off. When mine were young, they'd race
around like crazy and then pant for a minute or two.

However, these are newborn kittens. They should not yet need to pant to cool
themselves. It may be too warm where they are (unlikely, IMO), or they may be
in distress. Can you get them to a vet? I'd advise a thorough checkup for
these guys and for momma kitty. Can you tell if she is nursing them and if
she has enough milk? You may need to supplement with KMR.

When Francis was handed to me at four weeks, he would open his mouth to
cry, but the sound was so high pitched it was barely discernable.  Is
there a possibility these tykes are just crying, but you can't hear
them?  Those vocal cords are really tiny.

Priscilla