[quote=Harry Potter Wiki]It takes skill, practice, and patience for wizards and witches to become Animagi. The process of becoming an Animagus is long and arduous, and has the potential to backfire and cause the transformation to go horribly wrong, such as permanent half-human, half-animal mutations if done incorrectly. [i][b]Many witches and wizards simply feel that their time might better be employed in other ways, as the skill is of limited practical use unless one has a great need of disguise or concealment[/b][/i]. Part of the process by which one becomes an Animagus is holding the leaf of a mandrake in their mouth for an entire month, using the leaf for the creation of a potion, and reciting an incantation (Amato Animo Animato Animagus) on a daily basis. If the leaf is removed or swallowed, the witch or wizard will have to start over again.

At the next visible full moon (if the night happens to be cloudy one will have to start over), the wizard must spit the leaf in a phial within range of the moon's pure rays. To the moon-struck phial, the wizard or witch must add one of their own hairs, a silver teaspoon of dew that has not seen sunlight or been touched by human feet for seven days, and the chrysalis of a Death's-head Hawk Moth. The mixture must be put in a quiet, dark place and not be in any way disturbed. The next thing that must happen is for the wizard to wait for an electrical storm, whenever that might be. During this waiting period the wizard must, at sunrise and sundown without fail, chant the incantation Amato Animo Animato Animagus with the tip of their wand placed over the heart. When, at last, there is a lightening storm, the wizard ought to move immediately to a large and secure place, recite the incantation one final time, and then drink the potion.[/quote]

TL;DR Parents making their kids unregistered animagi is something Wizard CPS will take your kids away for, aside from being ludicrously difficult and almost completely pointless.