oh the memories, i remember being like 8 and finding my dad's stashes around the house, and not knowing what it was i would show my mom (who would get mad at me but only cause she didnt know how to tell me and my brother). This happened for a few years, me and my brother would always come across little baggies of buds here and there and one day in the winter we went to go shovel and there was a big baggie in one of the gloves and my brother pulled it out in front of my dad so they told us then... after that my dad was alot more relaxed about it, we never smoked together at the time but we knew where all the plants were in the bush. it actually wasnt untill a few years ago when me and my dad first smoked together. It was very awkward at first, but now whenever im home or if my parents are visiting me we always blaze, its great.
Alot of people would be surprised by the amount of people that smoke weed or once have. After my dad came clean to me and my brother we soon learnt that nearly all the adult population in our little community were stoners, im sure its the same in alot of other places too.

Either way dont do anything stupid like calling him a hypocrit or anything, just find a way to let him know you know. and then one day when hes stressed as fuck tell him you have a blunt with his name on it.