I free feed my puppy .If you leave food and water down all the time then your puppy will eat when hungry. You can still measure out the food daily to keep track of how much he/she is eating. Yorkie's have tiny stomachs and can only hold so much in, however they can get hungry sooner too.
I got my puppy at 9 weeks. since yo have a tiny baby you really do need to make sure he is eating enough all the time so he does not experience low blood sugar.