With 9 grandkids it is impossible to be at every birthday party, especially since most parties weren't planned well in advance. DH and I take the birthday grandkid out for lunch and shopping, that way if we had to miss the party we still did something special for their birthday. Grandkids range from 11 to 28 so it's usually lunch or dinner and a check or gift card and they do their own shopping now.
Have to start the cycle over again as our first great grandchild is expected to arrive end of August.