The New York Times has a colourful piece on a Colorado Springs Purity Ball.
These balls are substitutes for proms, with heavy spiritual themes and are a booming business for the abstinence only crowd.

This Colorado ball has been run for 10 years by Randy Wilson, the national field director of church ministries for the Family Research Council. Girls from grade school to high school go; step fathers, fathers or future father-in-laws are their ‘date. Abstinence studies indicate most teen participants break their vows and are far less likely than peers to use condoms.

Each father and his daughter walked under the arch and knelt before the cross. Synthesized hymns played. The fathers sometimes held their daughters and whispered a short prayer, and then the girls each placed a white rose, representing purity, at the foot of the cross. Mr. Lee and Rachel walked away holding hands.

The girls, many wearing purity rings, made silent vows. “I promise to God and myself and my family that I will stay pure in my thoughts and actions until I marry,” said Katie Swindler, 16.

Her father, Jim, said he brought her to show her how much he cherished her after almost losing her in a car accident two years ago.

The piece is not unsympathetic to the participants and hits a key note:

Loss tinged many at the ball. Stephen Clark, 64, came to the ball for the first time with Ashley Avery, 17, who is “promised” to his son, Zane, 16. Mr. Clark brought Ashley, in her white satin gown, to show her that he loved her like a daughter, he said, something he felt he needed to underscore after Ashley’s father left her family a year ago.

Mrs. Wilson, the organizer, said that her father abandoned her family when she was 2, and that Mr. Wilson’s father was distant. One father said he had terminal cancer and came with his two daughters. Others were trying to do better in their second marriages.

The NY Times accompanying slide show touches on what some see of the creepiness of the sub-culture Purity Ball movement. I think a few of the pictures rather enforce these events are held more for the men.

Abstinence Clearinghouse
Purity Ball kits

I have yet to see any of these companies selling dance kits for putting on mother/son purity balls.

Here is a news report on a 2007 Care Net Purity Ball.