We never had a tradition of writing a thank you note, being together on the day a hug and kiss after receiving a present, before opening it, is how we treated this.

When we moved further away and did not see the nieces and nephews over special holiday events, we made sure to wrap a special gift when visiting to make up for times not spent together, so once again it was when you could thank family.

Fall-outs are always difficult, children should never be included into adult disagreements, alas it does happen.