I am wondering the same thing.

+1. What's wrong abiut it?

I agree

My best guess: спать is used as an infinitive verb (to sleep) while your English answer is using sleep as an unaccountable noun. I'm new to language structure jargon, soooo...please correct me if I'm mistaken :-)

Dative case "Кому?"
Who needs more sleep? This boy... Therefore the subject is altered "Етому Мальчику" If not... no subject is defined and it could be... Sleep needs more boy.

This is the case system as I understand it... but I am also just grasping this idea so I could be incorrect.

Abbreviating "have" like this (should've = should have) is only done when "have" is used as an auxiliary verb in a compound verb, such as "should have gone" or "should've gone". Even then, it's very colloquial English, and Duo shouldn't accept it even when correctly used.

No, that sentence is grammatically sound.