Harry had expected de-aging to feel like something, and the tingling did that. The ChronoSwap felt warm in his hands with the fan going, and with his height, muscles, and body hair withdrawing it was no surprise to him that his little guy was also shrinking... and shrinking and- Henry took a glance at Henriette who was growing as was a little expected, but instead of growing maybe an inch and a bit outwards with her curves she was gaining a foot at least in height and her body was bulking out. Henry and Henriette had a chill down their spine as Henry's little buddy shrank out of existence, and while Henriette's ladies had turned to pecs she was also gaining a new buddy herself.
Henry was swimming in his clothes like he somewhat expected, but she wasn't expecting to be a girl. Henriette however bellowed in a baritone "The Heck?!? This was age why am I a dude?"
Sally hypothesized "...Something about not following the cooldown, maybe they didn't mean cooldown literally?"
Henry took a breath then squeaked out "We'll bring the ChronoSwap, the whole birthday party is funded by the company and they'll have some people keep an eye. We can say this little side effect happened and maybe... They can reproduce it and fix this?"
Their father said "For sure we shouldn't mess with the ChronoSwap right now. We'll have to see what happens."
"But Dad, I've got a date. I may have been able to swing looking a little young, but I can't date him like this!" Henriette complained
"We don't know what exactly caused your sexes to switch, using the ChronoSwap more could have even more disasterous effects."
"We're going to have to deal with this sis. I hope it can be resolved during the birthday party or just after," The sexes weren't that different before puberty, but going to school as a 16 year old girl felt like it'd be a real hassle Henry imagined. "It may not be a date, but you could at least hang out with him. See him when he's with other guys or something."
The two resolved themselves that they'd try to make the best out of this situation. Meanwhile Sally was thinking about what she was going to say to her friends... or how this would all end up working out.