May a child check eggs for blood?
Any child who [has reached the age of Chinuch and] knows how to check eggs for blood, may be trusted to check an egg for blood even if they are below the age of Bar/Bas Mitzvah. This applies to both fertilized and unfertilized eggs. This applies whether the child is checking the eggs for himself, or on behalf of others. A child who is not yet old enough to know how to properly check eggs for blood, may not be entrusted to do so.
 See Admur 432/10 [Child may be trusted with Rabbinical matter even initially and even no Mitzvah Min Hamuvchar to not trust him if does not involve any trouble] and so rules: Chok Yaakov 43/10; Elya Raba 432/6; Maharil Bedikas Chameitz 12/43; Michaber 437/4 and Pesachim 4a [If a child checked home is trusted]; Michaber and Rama Y.D. 66/8 [There is no obligation to check eggs for blood, and is just a Minhag]; Michaber Y.D. 66/4-7 [All bloods of Mufaros [unfertilized eggs] are only Rabbinical due to Maaras Ayinm, and the vast majority of eggs today are Muzaros]; See Hakashrus 13/26
May children be entrusted with the Kashrus of an item? Children below the age of Bar/Bas Mitzvah may not be entrusted with any Biblical matter. [Admur 437/10; Michaber 437/4; Y.D. 120/14] Children who have reached an age of understanding and responsibility may be trusted for all Rabbinical matters. [Admur 432/10; Michaber 437/4; Pesachim 4a; Rav Akiva Eiger Y.D. 120] They may be trusted even initially. [Admur 432/10; Chok Yaakov 43/10; Elya Raba 432/6; Maharil Bedikas Chameitz 12/43] If the matter does not involve any trouble, and there is no worry that they will be too lazy to do a proper job, there is no even Mitzvah Min Hamuvchar involved in having an adult do it. [Implication of Admur 432/10] They may be trusted even initially as an emissary, to do the Mitzvah on another’s behalf. [Admur and Poskim ibid, unlike Rav Akiva Eiger ibid]
Is the blood found in eggs Biblical or Rabbinical? This depends on the type of egg [fertilized versus unfertilized] and the area of the egg in which the blood was found. [See Michaber Y.D. 66/4-7] Unfertilized eggs, which is the majority of eggs on the market today, do not contain Biblically forbidden blood. [Michaber Y.D. 66/7; See Yabia Omer 3/2; Yechaveh Daas 3/57; Igros Moshe 36; Minchas Yitzchak 4/56]
Is one obligated to check eggs for blood? From the letter of the law, one is not required to check eggs for blood as we follow the majority of eggs which do not contain blood. [Michaber and Rama Y.D. 66/8; Hagahos Maimanis; Aruch] Nevertheless, the custom is to check all eggs that are placed into foods during the day to check if they have blood. [Rama ibid]
 M”B 437/19
 The reason: As children may be trusted with all Rabbinical matters, and the blood found in today’s eggs which are unfertilized is only Rabbinically forbidden due to Maaras Ayin. This in addition to the fact that from the letter of the law there is no need to check even fertilized eggs for blood, and it is a mere custom.
 The reason: As even fertilized eggs which may contain Biblical blood there is no need from the letter of the law to check the eggs for blood, as majority of eggs do not have blood. [Michaber and Rama Y.D. 66/8]
 Admur 432/10; Chok Yaakov 43/10; Elya Raba 432/6; Maharil Bedikas Chameitz 12/43
Other opinions: Some Poskim rule a child may not initially be entrusted to fulfill a Rabbinical command on behalf of another. [See Rebbe Akiva Eiger Y.D. 120]
 Admur 432/10; Michaber 437/4