Because The Regular Terrors Of Old Age Are Just Not Enough
When I first heard of this holiday, my mind conjured up images of middle-aged people bringing their geriatric, doddering parents to frolic in the playground, as those senior citizens slowly slipped towards their second childhood. As it turned out, the holiday is about the importance of play for children under the age of 12. The 'bring the parents along' part is presumably about increasing parent-children bonding opportunities.
While I agree it is important for young children to play, I think us older folks need to remember how to have fun too. As they say, all work and no play make Jack a dull boy. So get some games and toys and try to see if you can rediscover that inner-child.