I don't see anything wrong with letting him know you will be doing cake, etc for D's birthday and he is welcome to join in if he wants. Then leave it to him to decide.
I agree. I'd wait as long as possible, re: letting him know.. Be interesting to see if he inquires as to what you'll be doing for DD's BD.
Gardener
"My soul, be satisfied with flowers, With fruit, with weeds even; but gather them In the one garden you may call your own." Cyrano deBergerac
