My guyfriend of six months had his grandsons for the weekend and to meet me also,but not so good. Suggestions?

I tried several tactics,including just removing myself for a day to give them their space.We all went to a family dance for New Years,I read to the one who allowed me to,I stayed out of the way and just tried to be pleasant and helpful,as one has a badly broken leg.I feel they've heard stuff from his ex (their gramma), but he is so sure it's not happened, yeah right. I've never encountered this much hostility from any of my previous bf's children or grandchildren,Right now,I'm just relieved they went home; however I would appreciate suggestions for our next encounter to possibly/hopefully be better.for all.