7 week old chick,, Cant Balance,, Droopy wings,, and huddled

[Frisco]

I've got 2,, 7 week old chick who cant balance has a droopy wing and is huddled together i had one later Yesterday who had this then just died gave it Vitamins,, Apple cider and chick crumb and it didn't eat and 3 hours later it died,, There is now 2 who seem to be going this way,, Also i have 11 week old Chicks one which goes like this i bring her in and give her Vitamins,, water and food and its okay inside for 3 days i let it out and then goes back about a day after to its previous state,, know i have another one which is in the same pen as the previous one and she is now looking like she is going that way,,
My question is What is it ,, And how do i treat it??
P.S They haven't been wormed cause i don't worm them until 3 months old then every 3 months after that
Thank you in Advance if you If you could help me please.

 

[minharopaola]

Mine too is experiencing the same thing and they're about the same age. Ugh.

 

[PowellAnimals]

Is it possible they have Marek's disease or have they been vaccinated?