Q. My child is in a rebellious mood and won’t come to the Seder. What should I do?
A. When the Baal Shem Tov was asked a similar question, he said, “Love him all the more!”
You can’t force anyone to come to the Seder, nor should you bribe them or use threats or emotional blackmail. All sorts of reasons lead people (not necessarily, but often, the young) to make a statement by staying away from Seder or Yom Kippur.
The most you can and should do is to inform them gently but clearly that Seder is on such-and-such a night and that you’d be very happy to have the whole family there.
But if someone doesn’t come, they don’t come (an old lady I knew used to say, “If they don’t come, they don’t have to go home!”).
Almost always the child who stayed away is back by next year or sometime in the future.
When that time comes, one should not indulge in sarcasm at their expense (“So you finally decided to come, did you?”).
Much as we traditionalists don’t always like it, everyone has to work through their own Jewish identity crisis.