The door hits the jamb and will not close. What to do?

I recently had my basement finished with a bedroom and a walk-in closet. The contractors installed pre-hung (white) 6 panel doors. I purchased Kwikset locks for the doors and installed them last night. The passage lock on the closet worked great. However, on the locking bedroom door, (that opens inside the room) when you shut the door and it latches, you can push on the door from the outside and it opens. My 20 month daughter was the one that brought it to my attention. Can anyone tell me what it causing this and how to remedy it? The hole for the strike seeems to be large enough to accomidate the latch and you can here the latch extend into the strike when the door is closed. Any advice would greatly be appreciated. Thank you