A better close up photo of an individual poop would make assessment more accurate. What are you feeding them? Is it medicated feed? How are they acting? Coccidiosis will make them hunched and lethargic, so if they are looking active and normal I wouldn't worry too much but it may pay to have some Corid on hand in case they do suddenly start to show symptoms. I bought a little bottle marketed for pigeons a few years ago and thankfully have never had to use it but worth having as an insurance policy because cocci can kill quite quickly when it strikes and better to have the medicine on hand and start treating them the moment they look sick, than have to start driving around trying to find some when you need it.
Regards
Barbara
PS. At 4 weeks old worms would be extremely unlikely, particularly as they have only just been exposed to the outside world. The likelihood is that it is shed intestinal lining, but I really can't make it out from that photo.