It would be helpful to know why your son went to the allergy clinic and whether it was a clinic in an NHS hospital or equivalent. I note he went with his sister which may indicate it was a just in case visit
If he has just been routinely tested but never had a reaction he is in a different situation from having had anaphylaxis.
Some private clinics seem to never get a negative response, so you might be want to discuss the results with your GP to ensure the written report is shall we say up to scratch! There may not be the problem you think.......