From Pr. Weedon's blog:
The Great O Antiphons, used to frame the Magnificat in Vespers in the days before Christmas, begin [this] evening with O Wisdom. The Treasury [of Daily Prayer] includes them in the daily propers section. As each of these Old Testament names for God is prayed, and Christ is invoked to come to us, the clarity of whom the Blessed Mother bore is driven home in an unmistakable way, climaxing in the confession that He is Emmanuel, God with us. The Latin titles read backwards announce: ERO CRAS - I'll be [here] tomorrow, which is very fitting as the O Antiphons conclude upon December 23.
Here are some pretty coloring pages.