Ok, this is odd, I know it is and I will try to explain myself carefully because I in no way want to be taken out of context on this at all.
My son has recently started a new school, a primary. This is different to his old school in many ways, firstly because his last school was an infant school rather than a primary and because it also had an excellent, oversubscribed SENCO unit within the school, whereas this current one doesn't.
His last school was fabulous, just brilliant in the way it was run. I felt, still feel, it is very important to DSs general life experiences that he is aware of people with disabilities and the level of compassion he has shown from day 1 in reception, towards what are some very sick children makes me so proud.
In his old school, depending on the level of needs of the children in the SENCO unit, they either did or didn't join in with mainstream classes depending on capabilities, but in every other area was a very inclusive school and the children knew each other and played together alike. One of my sons best friends suffers severe global delay and has a lot of trouble socially and with learning but they became friends at this school and still remain so despite us having moved.
So onto new school, he is having a party and this school doesn't have a SENCO unit but does have several children with moderate learning difficulties as well as physical disabilities that attend school. My son is not friends with any of these children yet simply because he doesn't know them/hasn't met them.
A mother of one of the little boys with learning difficulties has found out that my DS is having a party and directly asked me why her DS was not invited? This little boy is in he same year, but in a different class and he is not the only one that has not been invited (out of the year), there are only 10 children coming to his party in total.
I tried to explain all of this to the mother (who I have never spoken with before) and she got very upset and said something along the lines of her DS doesn't get invited anywhere because of his disabilities and even the new boy (my DS) hasn't done so.
I feel so 
for both the DS and the mum who was quite upset about it, but my DS doesn't know him. Only by name and they've never even played together, and loads of other children aren't invited either.
I don't know what to do about this. What shall I do? As from my earlier details, its very obviously got sod all to do with the fact that this boy is disabled and I know she's upset but I feel quite miffed about the implication that he's not been invited because of his disabilities, when nothing could be further from the truth.
Genuinely confused and feeling bad and really don't know what to do.