You could make a big deal out of it just the two of you.
I'm not 100% on where you live but if you have something close you could do a day at the zoo, local pool, park.

I don't think we will get to do a party for DD2 this year, am thinking of saying to DP maybe we should go to the zoo, ask his mum & dad to come along etc.. not 100% if people will want to pay for themselves though IYKWIM.