Question: May you fulfill your mitzvah of daled minim with a dry lulav?
Short Answer: A dry lulav is pasul, even b’dieved. There is a dispute as to why a dry lulav is pasul. Nevertheless, we allow a dry lulavbish’as ha’d’chak.
Question: Must a father teach his young child to refrain from eating in part on Yom Kippur?
Short Answer: Yes. According to the Rambam, there is a chinuch obligation to teach a child to refrain from violating prohibitions, even if the child will not fully refrain from violating the prohibition.