Thank you for your query,
You can give Tylenol only in prescribed dosage for your child.
Tylenol PM contains diphenhydramine
in addition to tylenol and it will cause drowsiness
And there may be unpredictable allergic reaction
to a new drug which is not given early.
So consult your Pediatrician
for the examination of the child and treatment.
Hope I have answered your query.