My 3 year old daughter was watching me put a bunch of 50's and 60's cards in 9 pocket pages the other night. I mean watching intently. I can't say she understands baseball or my interest in cards yet, but she loves to sort stuff into containers of every kind (pots, bags, ziplocks, boxes, etc.). I think I saw a glimmer of interest in her eyes as she watched me sorting those cards. Maybe she'll be one of the people buying cards when she grows up.
Or not... who knows?