Funny you should mention that because I was going to consider tossing in a book or something - but yeah, playing cards might be ideal - also can be used for a variety of other tasks too.
I may include a colouring book and some crayons for my bro and his sis' bag - they have a 4 year old son.
For someone making one bag, you can definitely go with some more spendy, high-speed solutions. I know my personal kit is a bit more expensive, but I assembled most of it when money was no object. I'm not necessarily skimping on my family bags, but I'll leave it to them to flush it out or change things as needed.
My bag would have my Tops Prybar Knife, probably a spare ESEE etc. But I'm not dumping $200 worth of knives into each of these bags! I did end up ordering some emergency water rations (comes in a sealed bag). Just a couple. I'll brief the family members that in the dire emergency - especially if leaving a house, just grab another bag/backpack and toss as much food and water into it as you can.
Perhaps ask them to all keep a few gallons of water standing by with the bag in a closet or something.
PS: Yes, I am including some paper/markers/pens in the bag.