meea - grandson had a bone-scan last year. I can't offer you any suggestions re; occupying your DS whilst having the scan but I can give you a little more information about the procedure.
The so-called 'camera' is more like a tube shaped thing that slides over the person having the scan. It is very, very slow - we were lucky. GS was only five months and fell to sleep reasonably quickly. It is not actually very loud and I did find myself wanting to go to sleep in the room. There was one guy operating the machinery and anothet who occupied GS until he went to sleep - I have to say that they were fantastic with the baby.
And it's fascinating seeing your childs skeleton appearing on the screen. If the scan doesn't 'take' on one particular part of the body, they will do that bit again - so if he doesn't lay still, it may take a lot longer than the hour.
I don't want to upset you, but the 'injection' is not nice. It's a special fluid that enables the bones to show up on the scanner. GS's was administered through the back of his hand and he had to have a top-up a little while after. It's also radioactive - it won't hurt your little one, but apparently their wees and poohs are radioactive for a coule of days after and we were told to avoid pregnant women, and other children.
We had the same information re; attend for injection, then back in afternoon for scan. In reality, we were expected to stay and so were actually at the hospital all day. Might be an idea to take some lunch, etc.
It might be an idea to call and see if you will be allowed out between the injection and the scan.
Hope this helps somewhat.