Question

Which sentence contains a misspelled word?

Answer 1

Okay, so the word which was misspelled would be, 'peak'.
This is because the spelling of 'peak' relates to a mountain cliff
whereas the correct spelling would be 'peek. This is because you are
saying that you are checking on the baby. So therefore the last sentence contains the error.

Answer 2

Could you peak in the baby's room to make sure he's still in the crib?

In this situation it's not peak, it's peek. 
Peak is like the top of a mountain. 
Peek is like a glance.