Thank you for your query and sorry for replying to it so late.
I hope by now the leak of the cerebrospinal fluid
(CSF) must have stopped. If not then the doctors must have taken corrective measures.
It is not uncommon for the fluid to leak from the site where the drain has been removed as healing takes time. The neurosurgeon checked this by making your son cry which increases the CSF pressure and should have caused some leak if the healing was inadequate. As there was no leakage he did not take any corrective measures.
I hope I have answered your query to your satisfaction.
Wishing your son all the best.