[troubletb]

You should start brushing early, that way he gets use to it. I don't remember exactly when they start losing them but all of a sudden you will look at him and you will notice GOSH, He has no teeth!! You can not screw up, Just keep an eye on the incisors ( the long ones on either side, sometimes those don't fall out and have to be removed by your vet. Bell's did not fall out right away, the permanent teeth started to come in and they still didn't come loose, I was about to make an appointment and then one fell out, I waited another two weeks and the second one fell out also. Be patient.
I'm sure your a wonderful mom. and your doing a great job!
Good luck