SOLVED. group of close friends disappear one by one - turns out they are reptilian alien lizards [s]

[Chris]

This is a childrens/YA book from the 80's. There is a close group of 6 or 8 friends that live in the same town and either all share the exact same birthday or have their birthday within the same week. They are very close friends because of this and always celebrate their birthdays together. This year, as their (13th?, 16th?) birthday approaches (I thin they might have had a pool party), they start disappearing one by one until they have all gone missing. It turns out that the kids are really some kind of reptilian lizard-looking aliens that they have only just realized when they hit their (13th?, 16th?) birthday and matured. (Reptilian alien puberty, if you will.) I think the mothers were either impregnated by or injected while pregnant by the alien race.

The cover of the book showed one of the kids sitting in a car being startled by (what the reader sees as a reflection in the car window of) the reptilian alien.

Any help would be appreciated. Thanks!

[Chris]

SOLVED. Experiment in Terror by Bernal C. Payne.

[Lobstergirl, au gratin]

Experiment in Terror for the link.