There’s an invasion going on right under everyone's noses, very few know it’s happening and those who do, are in on it.
The invaders are the product of an experiment trying to reverse aging, the resulting new species being a hivemind collective made up of children, the Kidaliens.
The Kidaliens are shapeshifters, able to shape their bodies at a whim, although each Kidalien generally has a preferred shape, they can take on any form from humanoid slime to a tangled web of arms, legs and heads, the only rule is they can’t change their size.
Regardless of shape, a Kidalien is flexible in ways humans are not, near indestructible, and all of them are super geniuses, Kidaliens act as if made of rubber.
Kidaliens invade by pretending to be regular kids of around 5 to 8, they join elementary schools as transfer students and wait till they get alone with their schoolmates, once they do they offer to reveal their secret under the promise that if they don’t tell the adults, they promise to let them into a secret club.
Once the kids agree they show off their shapeshifting abilities and tell them that in time they can get those same abilities so long as the adults don’t find out, they then proceed to change their schoolmates into Kidaliens themselves.
A Kidalien changes a kid into a Kidalien by eating them, the Kidalien swallows the kid head first who will then find themselves in the Kidaliens stomach filled not with digestive enzymes but transformative ones, in the first minute the kid is connected to the Kidalien hivemind and within an hour they will become a full Kidalien.
Kidaliens then turn their siblings until only the adults and teens in the household remain, at which point the Kidaliens will beam their parents to the Kidalien mothership where they are melted down and converted into more Kidaliens while robot replicas of themselves will be put in their place that they will control.
One adult on average has enough mass to make one and a half Kidaliens, one teen has enough for one and a quarter, both are too big for a Kidalien to swallow whole.
There is no mind control or coercion here, aside from abducting the adults and turning them into living milkshakes, Kidaliens advertise themselves to other kids as Kids plus, no growing up, no getting hurt, and who doesn’t like being whatever you want? The Hivemind doesn’t destroy their individuality, just lets them coordinate better, Kidaliens are free to act however they like, adults are the same just with the added conditioning of very minor brainwashing to make them mentally kids again. (Can’t be too major, they’re controlling the robots.)
So you may ask; why? Why turn everyone into their own kind?
Why not, it’s fun! You should try it, it’s so fun to sneak into the schools, figure out just the right lie to get accepted as a student and watch all your new friends leave to change their parents!
Anyway, I’m going to melt you down now, don’t worry, it doesn’t hurt, I should know, I went through it twice, oh yeah, I forgot about that part, the extra mass from the adults and teens gets mixed together till you get a fusion of everyone who went into it, I’m basically a whole new person! Especially since there is a Kidalien for everyone who went into making me.
Oops, I’m rambling, I’ll start the machine now, I bet you’ll be delicious!