Although this is not classic Osgood Schlatter's the presentation appears similar albeit at a different location.

It would be key to understand the play habits/sporting/weight issues of this 12 year old. It might just well be growing pains with a bit of increased loading as a result, perhaps aggravating the patella tendon insertion to the patella.

Wikipedia reference-linkMRI is an OK thing to do to rule out other pathology and it is non-invasive. Does the boy have any other issues that could indicate he is seeking attention from the family members at this time?

I would do what you are doing for now. Rest, ice, reassurance that this is part of growing and if you like unload the tendon with some taping technique of your choice. See the effect of this and a review over one week and if symptoms are resolving then do nothing more. If they are not then let us know and we can think about other issues at that time.