I've set the expectation for my kids that my answer will be "no" if they've already asked Mom (this also helps out an end to the "go ask your father" redirect. If they ask me after Mom had already said "no", but hide the fact theyasked her already, then even if I say "yes" but later find out they played us, the answer becomes an absolute "no" also carries an additional "no" that would have otherwise been "yes" for future questions.