A lot of the ghosts have fucked up lore: Haunter spirits sad people away, Duskull spirits misbehaving children away, Driftloon grabs children and drags them to the afterlife, Gengar likes to hunt and kill people to create more ghosts, Yamask carries their death mask and cry when they see it, Phantump is a lost child that died in the woods, etc. etc.

Sinistea just steals the souls of whoever drinks it. Your probably confusing it with something like Drifloon who just straight up kidnaps children.

These Pokémon are called the "Signpost for Wandering Spirits." Children holding them sometimes vanish.