Of course, I imagine most of our dear readers will be celebrating the Motu Proprio with adult beverages, or fireworks, embassy balls, a Te Deum, courtly masques, Handel violin concertos and other such wonderfully refined entertainments, but let's not forget the kiddies, since they'll be the ones we'll have to be learning how to say Et cum spiritu tuo for those 5 AM low masses. (Girls, you're off the hook in this instance, but if you're lucky, maybe you'll grow up and get to be Catherine Pickstock or St. Joan of Arc or Emily of the Holy Whapping or the like.) In any case, here are some age-appropriate festivities for the little ones--or even your favorite gang of rowdy college students:

1. Pin the maniple on the subdeacon. Determine Gothic or Baroque vestments with liturgical arm-wrestling contest beforehand. Consult Dom Roulin on how to properly fasten this very pesky garment to everyone's favorite minor cleric. (If there are no relevant guidelines for liturgical arm-wrestling in the Pontificale, no doubt we can dig up some esoteric Irish monastic ritual to fill in the gap, like Ordeal by Club Sandwich or Trial by Magic Eight-Ball).*
2. Spin the aspergillum. Whoever "wins" has to exchange the Roman Pax with the person next to him--not so fun if played with elderly bingo ladies or seminarians, but great if you're sitting next to that cute girl from your sister's Legion of Mary group. Though in that case, best to play without alcohol, to be on the safe side.
3. Rubric or Dare. Either you cite the correct passage in Fortescue or you have to wear shoebuckles and a biretta to your next Novus Ordo at the Granola Hills World Peace Retirement Home.
4. Hunt the Buskin. Just in case one of your guests is a fully-vested bishop.
5. Ambrosian Liturgical Thurible-Lassoing Competition. Here's one for the Milanese three-sixty degree censer cowboy enthusiast in the audience. (Come now, you know there's at least one in every party.) A great way to rein in wayward lectors!
6. Toilet-Paper Cardinal. Extra points for the best train on his choir-cassock.
7. Musical Cathedras. If you have two (or more!) fully-vested bishops present at your party. More fun than a barrel of apostolic protonotaries de numero. This is reputedly the favorite party game of Cardinal Medina Estévez.
8. Incense boat-boy hazing rituals. Use up all that creativity you shouldn't be expending on mass! Remember that fire is our friend.
9. Low Mass Charades. Guess the saint, feastday, or papal name! For an additional challenge, conduct the game entirely sotto voce while facing the nearest mantelpiece.
10. Motu Mania Drinking Game. Comb news accounts of the famous document. Take one sip of the Veuve for the words "back to the people," "active participation," "nostalgia," or "ultraconservative." Take two sips for any reference to the Good Friday liturgy, "over-50 crowd," "body blow," "spirit of Vatican II," "un-pastoral," "tragedy," "in a dead language," "only in Latin," or "imminent schism." Four sips for "ultratraditionalist," or for mentioning that American congregations, who can sing "Pan de Vida" and Swahili hymns can't handle Latin. Down the whole bottle if the article concludes with the observation that civilization is about to end as a consequence.

*I made those up. The first club sandwich, after all, was invented at St. Gall based on directions in Vitruvius's eleventh book. It was shortly eaten by a laybrother named Wipo who was on his tea break and just wanted to try a bite but discovered he had no self control, and the recipe was lost until the Enlightenment. Meanwhile, it appears that while the Magic Eight Ball was invented in Song Dynasty China, it did not become commonplace in Europe until it appeared in 14th century Spain among an obscure Qabalistic sect of rabbis who venerated billiards as a representation of the triumph of Adam Kadmon over primordial chaos. Situation cloudy, try back later.