Son sometimes wakes up way too early

Where does he sleep? If my son wakes up early, I just leave him on his crib and don't go inside his room. Usually, he goes back to bed.

My son knows how to climb out his crib and cries until I get him , he still wakes up in the middle of the night and wants milk but for some reason he woke up at 3 am thinking it was morning. I’m pregnant and need him to sleep throughout the night so when the new baby comes he knows. I’m thinking maybe switch him to a regular bed but unsure. And yes he will cosleep and that usually does the trick to get him to go to sleep with some milk but for some reason yesterday he was worried he’d miss out on something woke up so early!