Year 5, kids are aged 9-10. Late last year, one boy - 'Martin' befriended 'Joe'. Joe was already good friends with 'Fiona' and DS which Martin was opposed to as he was quite possessive and continually tried to turn Joe agains Fiona and DS.
At Joe's house one day, Martin and Joe set about making potions. It later transpired that Martin had got hold of some poisonous berries from Joe's garden which he put in the potion, as well as pissing in it. His idea was to put this potion in Fiona's water bottle at school. Joe's mum intervened. She mentioned it to Martin's mum who brushed it off with "boys will be boys."
At school, Martin would give Fiona and DS evil looks and whisper swear words.
At Christmas, Martin sent Joe a Xmas card saying "I hope you get everything you want for xmas, especially to assassinate Fiona and DS" and drew a picture of a sword with blood dripping from it.
The card was shown to school, I personally went up to school to express my concern, school spoke to Martin and Martin's parents, and that was the end of that.
Martin's parents never approached us parents and it has been a bit awkward since. No cheerful 'how are you's in the playground as usual.
Martin and Joe drifted apart. Martin then tried to befriend DS. Knowing how manipulative he can be, I warned DS to remain at a safe distance and told him about the card. Although DS was initially hurt/angry, over time he forgave him and actually likes playing with Martin.
For DS birthday celebrations, I am inviting 5 kids for a day out. DS really wants Martin to come. I'm not so sure. On one hand, it is his birthday and feel it should be his choice. Also, I've been quite concerned about Martin bullying DS and perhaps it would be better to get him on side. DS is meant to be going on a school trip in June, for a week away and I considered cancelling it when the poisonous berries things came out.
On the other hand, I don't think he really deserves an invite and as I said, things are a bit awkward with the parents, I'm not sure how they'd respond.
AIBU to tell DS he can't come?