Everybody in the world is struck with the same disease.

Anyone over 18 gets tired and soon falls unconscious. They remain this way for years and while in this state, they're bodies start to get really cold and they remain ageless with no need for food or water. (Food and water particles were attracted to them in this state and gravitated toward them to give them the small sustenance they needed.)

Anyone under 18, the disease affects their body while their minds continue to grow unaffected. Their body on the inside grows to the maturity of an 18 year old (an 18 year old man would have a penis barely larger than when the disease first affected him, but now that we was an adult it and his testicles were at the full maturity to produce sperm and get erect).

The rest of the of their outside bodies would remain the same shape and size as when the disease struck them (an 18 year old woman would have breasts barely larger than when the disease first affected her, but now they and her ovaries were able to lactate, produce eggs and have periods).

The parents awake when their children have reached full mental and sexual maturity, (some of the sons and daughters reach maturity at 21 or 19 but the earliest is 18).

The sons and daughters were adults but growing without parental guidance for this long has left them unruly and uneducated. Now that these parents are awake they try to instill good values but it's harder to do that now that their brains were a little more stubborn.