The gemara tells a story of a father who knew that beis din would force him to free his slave, so he was makneh his eved to his child since the beis din would not use physical force on a child, thereby protecting himself from freeing his slave. However, Rav Papa ruled that they should: a. set up a caretaker for the child, b. give the child some money, c. write a contract to free the eved. But, there is a major machlokes Rishonim exactly how the mechanics of this worked.
1. Rashi held that the caretaker is only there to make sure to evaluate the market value of the eved which is to be given to the child. The child is considered the owner of the eved on a d'oraysa level, and is able to sell the eved to himself on a d'oraysa level but also needs a shtar shichrur to permit the eved to a regular bas yisroel.
2. Tosafos agrees that the child is the owner of the eved on a d'oraysa level. However, Tosafos holds that the child has no way to relinquish his ownership of the eved because the takana of peutos being able to do mekach u'memkar is only d'rabonon and based on hefeker beis din. The freeing of the eved is not accomplished by the child, rather by the caretaker. But Rabbeinu Shmuel and Rabbeinu Tam argue how the eved is freed. Rabbeinu Shmuel says that we penalize the owner by taking the eved from the child and giving him to the caretaker who frees him. The purpose of giving the child some money is simply so that they don't have to go against the will of the child who would otherwise be making a claim that the eved is his. Rabbeinu Tam holds that it is not a penalty, rather the caretaker has the authority to free the eved by selling him. Even the shatr shichrur is really not necessary me'ikar hadin, only a chumra m'drabonon.
3. Tosafos Rid holds that a child cannot even make an acquisition on a torah level. Therefore, the eved really belongs to the father m'doraysa, and to the child m'drabonon. There are 2 shtar shichrurs written, one by the child who we entice with money to write a contract to relinquish his rabbinin ownership, and the other is written by the father who we force to write a contract to relinquish his d'oraysa ownership.