Also, the FreeT3 and FReeT4 tests are direct measurements of thyroid
hormone. TSH is actually a pituitary
hormone, the message that the pituitary gland sends to the thyroid.
I've never heard of a child so young getting Hashimoto's thyroid disease, which will lead to low thyroid hormone, but the tests for that are the TPOab and the TGab.
Here's a wikipedia link on congenital hypothryoisim which happens to infants. http://en.wikipedia.