Maaser Sheni, Chapter Four, Mishnah Four
When a person redeems his own maaser sheni, he must add an extra fifth to the value, but when he redeems someone elses maaser sheni produce, he need not do so. Our mishnah teaches that there are ways in which a person can get around having to add the extra fifth, but that this does not always work.
1) One may act in a deceptive manner when it comes to maaser sheni.
2) How so? A man may say to his grown-up son or daughter, or to his Hebrew slave or female slave, Take this money and redeem this maaser sheni for yourself.
3) But he may not say so to his son or daughter who are minors or to his Canaanite slave or female slave, because their hand is as his own hand.
Section one: It is possible to act in a deceptive manner when it comes to maaser sheni so that one can get out of paying the added fifth.
Section two: One is able to give money to ones adult children or Hebrew slave in order for them to redeem the maaser sheni, as long as he says, redeem this maaser sheni for yourself. Even if the child or slave gives the produce back to the father and gives him back the maaser sheni money so that the father can bring it to Jerusalem, this is possible, because adult children and Hebrew slaves are independent of their father/master. These people can independently own property. So this is considered a case of one person redeeming someone elses maaser sheni, and he does not need to add the extra fifth.
Section three: In contrast, minors and non-Jewish slaves (called Canaanite slaves) cannot legally own property. Any money they make or any thing they find automatically belongs to the father/master. Therefore, when he gives them money to redeem maaser sheni, it is as if he is redeeming it himself, and he still needs to add the extra fifth.