My first thought is usually one of the parents is too young
but I don't think that is so with yours.
Have you taken the parents for a vet check? If there is a
health issue this needs to be cleared of course.
When I put up nest boxes I give adult birds apple cider
vinegar for 3 days to help flush out any minor bacteria. 5
drops of acv in 8 oz of water. I might give it to them
again just before babys are to hatch for just 1 day. I am
getting better at giving it to all the birds for one day
once a month instead of every 5 or 6 weeks :-)
The only baby tiel I lost to crop problem I too pulled at
about 5 days old when I saw it in the nest too full when
others were not. After a vet visit and doing all necessary
it died after a week. That's when I learned to use the tube
with syringe to suction the crop. Not easy but it was
necessary so I didn't have to keep going to the vet. Since
then I've heard fresh papaya mashed/pureed will help flush
the crop. This is mixed with a tiny bit of water all same
temp as formula would be.
I do think the parents sence something wrong but we have
saved so many of these babys and that's a good thing.
Your 5 week old one could have aspirated on food. They drop
so many seeds while learning to hull them could be one went
down the wrong way with the baby trying not to drop it.
So very sorry Beth.