137:9 Two people who jointly purchase the four species presumably do so with the understanding at the time of the purchase that when performing the mitzvah, each acquires the other’s share (though it’s preferable to verbally express this when performing the mitzvah – Mishnah Brurah 658:32). From here we have the practice for the congregation to buy the four species for anyone to use for purposes of the mitzvah. Anyone who can afford to is obligated to contribute towards this communal set. (If one was able to contribute and didn’t, he does not fulfill his obligation by using this set – MB 658:38.) Despite all this, it is best to perform the mitzvah with privately-owned species, provided they are of very high quality. This is because what one individual transfers to another is better.
137:10 One should not allow children to take the lulav and esrog on the first day of Succos (two days outside of Israel – MB 658:23) until after the adults have used it. This is because under halacha a child can legally acquire something but he can’t transfer ownership back.