How many babies would know what comfy means? How many people ask a baby if they are comfy? This question is usually asked when expecting a response. Why would this be asked to a baby?
OP you have issues. Why does anyone care what words anyone else uses? Comfy is pretty well accepted as a colloquial contraction of "comfortable". It's even in the dictionary:
According to the OED, it was first attested in writing in 1829, though that means it was surely used informally for quite a while before. In a related note, "comfily" was first used in 1917.