start young, my son is two and half and we've already taught him his arabic alphabet and numbers 1-10 and he knows many of the prophet's names from listening to us read to him.
he can also recognise most numbers and letters, for the letters this site is really useful
(but through this he is also very good with a mouse and computer and have to lock the pc otherwise i find all my files moved around when i come back)
we also teach him through question and answer, like asking him 'do you love mummy' and he will say yes or na'am then we'll ask but who do you love the most and he'll say ''Allah!''
so asking him who is his prophet - Muhammad (saws)
what is his book - Quran
who made him - Allah
what is he - muslim
what is his deen - islam
how many pillars in islam - 5
what is the first pillar, 2nd pillar etc - shahadah, salaah etc
where does he want to go - jannah
just simple little things like this and he learns and picks it up so quickly.
when he hears music he will already say 'music haram daddy, music haram'
or just be walking down the street and point and say 'Allah made that' or 'Allah made the tree' or 'Allah made the sun' because he knows this as we told him Allah made everything and everyone.