Another GIMP user here.
There is also (free or paid for) software which will make a stab at colorizing (sic) black and white photos once they've been scanned.
ETA:
https://colourise.sg/#colorize is a free web-based version.
I think that it works something like:
- anything textured in the foreground is green (grass)
- anything smooth at the top of the photo is blue (sky)
- anything recognised as a face is pink
- hair colour is hit and miss (blond is OK, but ginger isn't)
- clothes are guessed at - sometimes blue, sometimes a muted red whatever the original
but you can always retouch as desired.
Anyway, it means you can turn this
into
The grass is correct, as is the building in the background (both b/w stuff and brickwork). The woollen hoody thing was beigish, but the trike was blue.
or this
into
A furure PBP & LEL in those legs