Neo00779, no. it means directly to the boys. With ninos, they mean boys on this it is not correct to say the kids sleep because... Well. It's what it means. Also, while niños means them all, it's not correct because it means in this case, one gender, kids or children do not show one gender as they need you to give them. they can mean boys, girls, or both. There is no certain gender in those two words and it means the boys sleep while that is perfectly ok for your own opinion, it is incorrect for what Duolingo wants you to answer. And Duo can get pretty tight when he wants one certain word that is not being given. I hope this helped and I wish you the best of luck when you do this lesson again! :D
All verbs have lots of tenses grouped in Indicative, Subjunctive and Imperative.
A general rule (to have something in hand):
Imperative for commands (in affirmative) Subjunctive (negative commands, most subordinated sentences, expressing possibilities, expectations, ...) Indicative: just normal sentences...