Collecting old coins as a hobby

He started collecting old coins about a year ago. I've found my collection of invalid coins from childhood and I'm continuing to expand my collection. I have old German brands of East German Marks, Russian Rubles, Czechoslovak Crown, Polish zloty, Yugoslav dinare. I started collecting and I picked up banknotes from countries where I would never go, but collecting a little as I travel. I also have my 7 year old son involved in his hobby, I hope he will keep that enthusiasm as long as possible. Share your collections too.