Can you give us more info on where you keep them, what are they standing on, what type of heat, etc....
Many things can contribute to death and can be difficult to tell. here are some tips.
Keep peachicks off the ground until at least 3 months old.
Make sure they are eating a good quality turkey/gamebird starter etc.
Make sure they have plenty of room. They need more space then baby chicks as they jump and bounce at an earlier age and are more energetic and can jump high and can run over younger chicks.
Make sure they are out of drafts and also they do not get too hot.
If you see one getting weak, separate them. Give them scrambled eggs, soft canned dog food or handfeeding formula etc. for extra
energy. If they were housed with chicks they could have coccidia, if showing droopiness, weakness and overall disinterest.