Fine hair, DRY scalp

My son has very dry scalp, but has fine, biracial hair that's closer to caucasian hair than African hair. I have course, African hair.

I can't use products on his scalp that I use on my own because it's too heavy for his hair and makes his hair greasy.

What would you fine haired people recommend I put on his dry scalp that won't weigh his hair down?

My husband and his family have no idea because they have fine hair with an oily scalp.

I don't know how much help I can be, but I'm a Caucasian with fine, normal hair and a dry scalp.
At night, I drip a few drops of jojoba oil into my hands and give my scalp a good massage with it.  It makes the roots oily, a bit, but my scalp is happy and non-itchy for the first time in years.  You can also try adding essential oils to the jojoba oil - it's very light and has almost no scent.  I now use a mixture of jojoba with birch and rosemary essential oils that seems to work for me just fine.
I also switched shampoos to Giovanni's Tea Tree shampoo and conditioner.  This is the first time I have been able to shampoo two days in a row and not end up with a hoplelessly itchy head.
I hope this is at least a little helpful - I'd try some jojoba before anything else, if you can get him to sit still long enough to have his head rubbed!

Kirea wrote: Even if your son is a young child, adult shampoos are just fine to use if you avoid the eyes. Baby shampoo is actually quite harsh- the ingredients they use to make it 'no tears' are very strong.

I'm with Kirea - even the California Baby line, which is really gentle, made my dry scalp itch.  I thought I'd try baby shampoos for a while and MAN, those things can be harsh.
If you want to try a little bit of the Giovanni Tea Tree without making a big committment, PM me and I'll send you a sample.  I ended up with two of the shampoos in a trade - when what I really needed was two conditioners!  I can also send you a little bit of the Aubrey organic jojoba, which comes in a little tiny bottle and came for free with one of my Aubrey purchases.  I've used a little of it, but not much, since I tend to really glop it on and this bottle is just too little for that purpose.  If you think it would help your little sproglet and his dry scalp, I'd be happy to send it along and further clear out my product graveyard.
Let me know.