Children's Benadryl's own label says not to use it for sleep
It is the first line of the Do Not Use section on the 12.5 mg per 5 mL allergy liquid, which also warns that excitability may occur, especially in children.
What the study found
Do not use to make a child sleepy is printed on the label
It is the first line of the Do Not Use section on Children's Benadryl Allergy, a diphenhydramine liquid at 12.5 mg per 5 mL. The same label warns that excitability may occur, especially in children, and its chart permits no dose under 2 years and none from 2 to 5 without a doctor.
The caveat · The allergy liquid's label only
The instruction sits on the allergy liquid. The dedicated sleep aids handle the question differently, by excluding anyone under 12 outright, so the sentence belongs to this label, not to diphenhydramine labelling in general. A label requirement is not evidence about how often harm follows.