Online attendance system
Generate a list of unique coupon codes in a format of your choice.
Print them out prior to the meeting /event/ ceremony. Like lottery tickets.
Hand them out to attendees, one for each kid. At the end I guess.
Each kid then later enters the coupon code into a website to confirm attendance.
Repeat prior to the next event...


There's a question here regarding preparation of coupons.  Just formulate your generation algorithm carefully to avoid BUMH0LEs.