Put the little ones to bed, invite some grown ups over and open up a bottle or 2!?
Your baby couldn't give a flying fig about his birthday and the person who deserves the credit for keeping him alive this long is you. By all means have a cake and a few rounds of "Happy Birthday" at baby group but save the celebration for the ones who'll remember it.
Cheers! And well done for surviving this difficult year with enough energy to even think about a birthday party!