Translation:You are childish!
Childlike is aniñado. A virtue, sometimes. Childish is infantil, pueril. Not so virtuous.
la respuesta que mi mente buscaba, gracias mitcorb! por favor, recibe este lingot!!
Etimología español: foot soldiers are called infantry because the first regiments were named for las infantas, the official title of children of the Spanish monarch.
Okay, that explains why King Louis XIV's Spanish wife was referred to as the Infanta. (Obscure reference alert!)
The old R vs L problem. I checked it and the R is there. True, the two can be very close to each other. You'll just have to train your ear more.
If you are translating a spoken sentence, try the slow speech setting. It can help a lot.
That doesn't mean it's incorrect, just that Duo doesn't yet recognize it.
This could be an answer, but in this context, 'infantil' is being used to criticize someone. Being 'young at heart' is usually a good thing, meaning that you like to play. Being childish in this translation means that your behavior is not very good.
It counted "You're being childish!" as wrong and I understand why, but in American English the circumstances where you would say "You are childish!" instead are rare.
"You're being childish!" = a behavior that needs to be changed.
"You are childish!" = a permanent condition not subject to change.
What I am wondering is is the Spanish ¡Eres infantil! truly reflect the second meaning set.