Liz is an average height 8 year old at just under 4' tall, on her way home from school, she had a bad day because the boys were all bullying her for being too quiet, even the teachers had a tendency to get spooked by her, due to her meek nature.
Right around the corner from her house she noticed something lodged into the hedges at her neighbours, it was a small device that wasn't too dissimilar to a water pistol, but when she picked it up it definitely weighed more than one. there was a switch on the side like a small toggle reading (R) and (E), and it was currently set to (R) there was also a knob that ranged from 10-300, but it had been pushed past the 300 mark and seemingly broken there in place. Liz was investigating the weird device, played with the toggles a few times, and when she tried to use the knob the device began to become very hot and Liz dropped it on the ground, as it hit the ground it shattered into many pieces, most of which were warped and damaged by the intense heat, and it emitted a bright green flash that blinded Liz for a minute.
She looked around and saw that nobody had seen her touch the device and she could just walk home free of any blame for breaking it, and swept it into the bushes. Her evening went by fairly uneventfully, and she measured herself on her wall like she did every night and every morning. 4' this evening, she gained a centimeter since this morning. She got excited and could hardly sleep, but managed to get a good nights sleep after a good hour of excitement.
The next morning she awoke, and was more ravenous than she had ever been before in her life, so she skipped measuring herself and went right to breakfast, during which she could not stop talking about how she had grown, her parents had never been more excited to see a school bus.
After getting home from school that day she was feeling as if her clothes had gotten tighter throughout the day, when she went into her room to change she realized that her previous measurement on the wall was now at eye level, she remeasured herself and found that she was now 4' 5", and not only that, she felt as if her breasts were beginning to develop, but almost didn't know what to make of it at the time.
Liz's parents were out for the night so her aunt was babysitting, which meant she would plant herself on the couch and listen for any noises. So Liz stayed in her room for the majority of the night, while frequently running to the kitchen for snacks. When she ultimately got full, she was exhausted and passed out in her bed.
When she awoke the next day her feet were over the edge of her bed,and further more, she definitely noticed ever so slight chest development, not even close to A cup but certainly no longer as flat as a board.
She went to her measurement station and saw that she was now 5'10" and in her mirror she saw that she had changed proportions a bit through the night. She was more slender.
She knew that she couldn't let her parents see her like this and snuck out the window wearing the baggiest article of clothing she owned. She skipped school and by midday she had to sneak into the mall and find new clothes that would cover her changing frame. In the mall the baggy shirt was now barely covering her hips, and she was constantly tugging it downward.
She was drawing a lot of attention to herself, She found her way to the Big and tall store and asked to be measured for fitting clothes, the saleswoman had to turn her away, as they didn't have clothes for people over 8 feet tall.
"I'm not eight feet tall!" said Liz as the shirt she was struggling to keep down finally tore, revealing her still not A cup but certainly bigger than this morning chest.
"I have you measured at 8'6"! and if you could please contain yourself you are scaring off our clients!" said the shopkeep, but Liz looked around at the hordes of gawking men and begged to differ.
She knew exactly what was causing this, and started heading back to her neighbours house. On her way she...
( moderation note - Edited 1/29/17 at 4:57 AM
Please keep proportions reasonable and don't overdo the breast thing thing please. )