Digital cameras come with different sized sensors that are what captures the image. Generally speaking, bigger sensors can capture more detail, so better image. But not as simple as that, because it also depends on the processor inside the camera on how it alters the image and the quality of the lens.
SLR cameras have a mirror to allow you to look through the lens to see the exact image you will photograph.
Mirror less cameras have advantage of more compact. (Sony and Fuji worth a look).
Most SLR and mirror less and some of the better compact cameras use an APS sized sensor which is much larger than those inside typical small cameras.
Some professional and semi professional cameras use a full frame sensor that is similar to the old 35mm film image.
Bridge cameras look similar to SLR cameras but many use a small sensor (some do have larger APS) and have advantage of large lens and tend to be very inexpensive.
If your son wants to own a creative camera other than a good phone camera, maybe go for Bridge camera at £100 to £200 range.
Do not spend a lot of money unless you think your son is definitely going to be capable and enthusiastic about using it.
I have a Nikon D7200 kit, (about £1000) which is a semi professional camera in many points, but difficult to use if not experienced with it.
For to be part of the crowd and avoiding heavy large cameras, it is best to have a smallish camera. Even many Professional photographers use compact cameras, - some solely