Children can play but they must have an adult (18+) present with their key to the world card if they happen to win.
On my last 7 night cruise in August, prices for the early sessions were $30/6 paper cards, $40/24 electronic cards, $50/48 electronic cards, and a family pack for $80/2x24 electronic cards and 2x6 paper cards. One session in the middle of the week you got double the # of cards for the same price, and for the final session the prices changed - there was no more family pack - you could buy 6 paper cards for $40, or 36/72 electronic cards for $70/90, with a $10 loyalty discount if you played at least 3 times before the final session.
Hope this helps!
Aby