The river of science: Paul Samuel Jacobs, Born Into Light (London: Scholastic, 1988). However, I am pretty sure that the author is American.
Roger is ten years old when he and his fourteen year old sister Charlotte see a shooting star. Charlotte runs out into the storm and comes back with a "wild child", a young boy who, as they stare at him, becomes more and more like Roger.
Roger, Charlotte and their mother take the child in, despite the Doctor's warnings that he may never speak, and slowly but surely he picks up language and culture. Ben, as they name him: learns fast but is curiously literal and has huge gaps in his knowledge. When later the family rescues the chid Nell from an institution, she behaves in much the same way: less obviously curious but just as bright.
Most of the story is about Roger's experience of growing up with two "odd" children. Nell and Ben are, in today's terminology, mildly autistic. They have trouble reading social cues and metaphor rather passes them by. They are also very frail: Nell almost dies. Ben has special powers but is exhausted by their use. As they grow the family becomes aware of other "wild children". One, Montrose, is a school friend of Ben's but dies after a sprint race which leaves Ben too ill to attend school. As the years go on, it also becomes obvious that the children, a few more of whom have been identified, age more rapidly than humans for it is now admitted by those who know them that they are probably not truly humans but faulty copies.
Ben and Roger, educated first by their step-father (the doctor) both grow up to be scientists. Ben becomes an astronomer and Roger a research doctor, and here is where the book adds a layer of complexity, for Father declares, "..for mankind, to know is also to live." (78) Yet despite its presentation of scientific enquiry as highly desirable, the book itself does not proceed in that manner. Roger, our pov, tells us in the end not o his enquiry, but of the story of enquiry that Ben told him. So that, as with too much of the modern science curriculum, science is replaced with the story of science, research with the story of research.
At the conclusion of the book, Roger tells us of his conclusions: after reading Ben's research and diaries, all of which point to an alien origin, to the need of another species for our gene pool (the hybrid children are taken off the planet during the conjunction of the pertinent stars) Roger decides that the wild children were the descendants of a pre-human species who vacated the planet earth and have now returned.
I cannot emphasize this enough: nowhere in the book or in Ben's notes is there any evidence for this. Suddenly, and without explanation, and in a way that is utterly out of character for the scientist-Roger, a Fortean explanation is thrown into the mix. It is as if, right at the very end, the author had to remind us that the way of knowing that is "the scientific method" was inherently untrustworthy. The heart not the head rules the episteme.
And we wonder why religious adherence is growing and we can't get kids to study science.