Soutenus pointed out the Sunday Stickers program. Basically, it's a little sticker album and each week the child places a sticker in it after they have attended Mass. It was designed to be use parish-wide but it can certainly be fun on a "family level" as well.
In the USA, the price for single copies is $7.50 for the year, which includes the album and the stickers for the year. They are taking pre-orders (pay nothing now) because they need to have orders for 2000 copies before going to print. Pre-orders can be made until September 7, and you won't be able to buy an album if you don't pre-order.
I ordered one for Little Brother and one for Adventure Boy.
And don't forget to check out Who's Behind It, which explains the origin of the idea and where the proceedss from these albums will go. Certainly a worthy cause! In fact, this is a non-profit venture done largely through volunteer labor, because they believe it's an important service.