Have not read the whole thread as I suspect it is very similar to other threads on vaccs. on here.
Some children have no reaction to MMR. Those are probably the children who, if you were to take blood from them at the booster MMR stage (3 and a half years approx) you would find have insufficient antibodies to MMR and who are not protected. You would very likely see a correlation between no reaction and insufficient antibodies.
Then there is the 'typical' reaction, 7-10 days post immunisation. This might be 3-4 days in duration, grumpy, maybe vomity, off food, maybe a rash and temperature, very similar to a typical virus.
Then you have the very 'robust' reactions which last 7 days + maybe 'mini-mumps' ie, nodes up in the neck, really miserable, high temp, quite poorly for a while.
It is a good idea to ask about possible reactions at the time of immunisation, not a good idea to get it done a week before Xmas for instance, be armed with Calpol or similar and expect some kind of reaction, forwarned is fore-armed.
It should be remembered it is not a bad thing if they react, their bodies are doing the right thing and building up antibodies/defences to the diseases.
In response to the poster who recommended the reaction should be reported to the doctor, I'm afraid the doctor would simply say, 'fine, that's exactly what the vaccine and the body should be doing...'
It is normal and even desirable to see some kind of reaction, though it is never nice to see your child unwell. Children will react in different ways and it is impossible to predict how they will behave.
Hope this helps.