The important thing to keep in mind is, that scaled down bassoons are transposing instruments, so they sound differently than they are notated. This means, that for ensemble play a different edition of sheet music is required.
I participate in an annual bassoon workshop with groups in all ages in Germany link to page, German only and there are many children choosing a sort of "children bassoon": the keys are adjusted to smaller hands, a few are not present at all (but can be supplemented later) and part of the wood is replaced by an acrylic tube, to save some weight, see manufacturer page. The advantage of this approach is, that it already sounds as notated, which I consider as an advantage to learn intonation. Also it is considered more cool (by children), since the low pitch is a substantial part of the bassoons personality.
My teacher says, that boys like this less than girls, because it does not look exactly like the real thing, but a tenoroon will be more different in any case.
Another option I tried for some minutes, is Fagonello, a one-part children variant more reminding to bassoon precursors, also sounding in original pitch.
In any case the fingering is very similar to the standard bassoon for all alternatives, and embouchure even more so, so any alternative will provide a good foundation for a future bassoonist.
My recommendation is: try the instruments in real (if possible, with the teacher). Sound, touch and feel are important than a high-gloss specification, because your son needs to have fun to devote many hours to playing.