Chicks that fail to thrive usually die in their first few days of hatching. There may be a malabsorptive problem where the chicks eat well enough, but the nutrition isn’t making it through. Bacteria are often a major causation.
---
When chicks die at several weeks old after seemingly feeding and growing normally it’s not really ‘failure to thrive’, but terminology isn’t as important as making sure it doesn’t happen again. The most common causation here is also bacteria, and surprisingly, the source is usually the parents.
---
Bacteria are easily transferred from adult through the porous shell of the egg. Bacteria that an adult’s immune system can handle, but that eventually claims the chicks (that’s why it can take weeks for them to succumb).
---
There are a great number of viruses that may also be present, so having a necropsy on any one of the young would be a good idea to help prevent future losses. Also (or instead), having a blood chemistry, cultures and fecal float done on the parents (or at least the hen) is the quickest way to know what to treat in most cases.
---
For a makeshift brooder, use a small box lined with soft clothes like tee shirts.

---
Use a thick, clean sock and fill it ¾ with plain, raw white rice. Knot the end and microwave it for about 1 ½ minutes.  Shake it afterwards to distribute the heat and be sure it's not too hot.  Tuck this in just under the cloths.
---
A heating pad under the box is also helpful, set on low.    

---

 If ever using an electric source for heating anything in anyway, please be vigilant and constantly double checking carefully.

---
Gently drape a light cover over this box to further help hold heat in and keep light low.
---
Feed some warm mash in very small amounts or (Human) baby rice cereal mixed as directed
---
 I really hope you make it through this.  Don't forget to have a vet at the ready if you notice the chick taking a turn for the worse.  Good luck, God bless.

-- I didn't think it would, but I understand that you needed to try. I'm so sorry for your loss. I know how easy it is to become attached to these birds.

When you are adding stock or just adopting pets, don't hesitate to ask if the source birds are vaccinated against prevalent diseases in your area, such as Marek’s Disease; Newcastle Disease; Infectious Bronchitis; Laryngotracheitis; Fowl Pox; Fowl Cholera and Avian encephalomyelitis.
---
With the exception of Marek’s Disease vaccination, all other vaccinations should be given to stock over 10 days old.
---
There are many more details including explanations of the diseases and where to get the vaccines here: http://edis.ifas.ufl.edu/ps030


------------

If I can ever help again just ask for "August" in your subject line, but rest assured that our other bird experts are top quality professionals as well.

Again, I'm sorry for your loss