childish

US /ˈtʃaɪl.dɪʃ/
UK /ˈtʃaɪl.dɪʃ/
"childish" picture
1.

of, like, or appropriate to a child

:
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She has a very childish handwriting.
•
His behavior was quite childish for his age.
:
immatureinfantilejuvenilepuerileadolescent