Our 10-month old boy just can't seem to be alone for a minute. He's crawling and pull-to-standing but not yet walking.

Whenever he can't see either his mom/dad/helper (actually anyone for that matter), he starts bawling non-stop until we go over and keep him company. Then he's totally fine doing whatever, so long as someone's next to him. The minute we get up and go to another room or try to do something else that's not in his visual range, he starts bawling again.

Help?!?! How can we train him to be more independent?