It would seem sensible to let potential adopters first 'train' themselves by becoming foster parents: They would need to be very closely supported and supervised by other, more experienced, possibly retired foster parents, and some 'proxy grannies'. They would also need to be subject to frequent proper checks.
Technology could make this cheaper and easier. As well as visits to the home, and as well as an obligation to take the baby/child to medical check-ups, people could be asked to switch on a home camera, to record both the good and the bad interactions with the child. This would not be to find fault. It would show where they are doing well, and where there are difficulties, so they can be helped and advised by others who have experienced exactly the same problems: Foster parents and adopters have the necessary expertise: Social workers do not.
Home visits should not, or not only, be carried out by the peculiarly inept 'social workers', but always with cynical experienced knowledgeable experts, i.e. other existing or retired foster parents, (but not the ones already known to the novice foster parents, so with no personal bias or investment in 'approving' everything the potential parents do, because they are strangers, and not easily conned by manipulative or plausible 'friends').
Preston's foster mother, and his grandmother, were correctly alarmed, and incorrectly ignored. NHS professionals, and the unspeakably complacent, ideologically 'captured' social workers, were easily fobbed off.
Remember Baby P, whose mother smeared chocolate spread over his face to conceal injuries? Seven previous babies had been taken from her, but nothing made the social worker suspicious.
Nothing at present obliges a parent or prospective parent to attend a medical centre for the child to be stripped and checked and weighed, as well as vaccinated, at appropriate intervals. (And of course signs of venereal disease or penetration in anus or mouth or vagina should be routinely looked for, by an all female medical staff, as well as checking for 'female circumcision' i.e. female 'castration'.)
Knowing this will happen, at intervals, including to children of birth parents, would prevent a lot of abuse in the first place. Sarah Sharma and other children 'punished' by beating, and including 'home-schooled' children, would have been protected to some extent by knowing the law bans harming children, and knowing that parents are not, in Britain, slave-owners of their children, free to do as they like, to their own human 'property' regardless of injury.