When we receive the communion, the Eucharist, we are participating in the holy banquet and feast which is the crucified Christ. This banquet is done in remembrance of Christ’s passion as well as for the remission of sins, and finally as to what the word ‘communion’ implies, to be in full and absolute communion (part of a community) with God the Father.
St. Paul speaks of the body being the temple of the Holy Spirit. (1 Cor 6:19) When a child is present inside the body, they are given only what the mother feeds them. A child in the womb is completely dependent on the mother for existence. This is what Christ means when he tells the deciles to “become as little children.” (Mat 18:3) The child, who is completely dependent on its mother, is the most humble creature. Christ goes on to say in Matthew that whoever humbles himself like a child is the greatest in the Kingdom of Heaven.
So when it comes to the question of whether the child is receiving the Eucharist when its mother consumes it, I would go as so far to say that instead everything the child receives is the Eucharist. The child is already residing in the Temple of the Holy Spirit, in complete communion with God, and is considered the greatest in the Kingdom of Heaven. If, for example, the mother were to break the fast, the child would not by default also be breaking the fast.
In the Orthodox Church, the baptism, chrismation, and what is referred to by Catholics as the “first communion” all happen during the same time, almost always during the Divine Liturgy, and most commonly within 40 days of the child’s birth. This does not mean that before this point, the child is not watched after by God. The child has already been given life and nourished in the temple of God for 9 months.
Often when infants die before they are baptized (during baptism they receive the title “the servant of God”) they are referred to by the Church as “Holy Innocents.” An example of this are the 14,000 Holy Innocents killed by King Herod in Bethlehem when Herod was looking to kill Christ. The Orthodox Church commemorates them as the first Martyrs of Christ and celebrates their feast day on December 29th (new calender) every year.
The Orthodox Church does not believe that infants go into limbo or are cast into hell because of original sin. The sin is simply our choice to disobey God. Children, especially those in the womb, do not choose to disobey God and are in perfect communion with Him. After the child leaves the womb and begins to mature, it is the responsibility of the parents, friends, and godparents (hence where the name comes from) to teach the child and to help it grow and fully love God.
Finally, concerning hell, I have posted the words of a Saint in the Orthodox Church, Isaac the Syrian (6th Century):
“Those who find themselves in Gehenna will be chastised with the scourge of Love. How cruel and bitter this torment of Love will be! For those who understand they have sinned against Love, undergo greater sufferings than those produced by the most fearful tortures. The sorrow which takes hold of the heart which has sinned against Love, is more piercing than any other pain! It is not right to say that the sinners in hell are deprived of the Love of God… but Love acts in two different ways: as suffering in the reproved, and as joy in the blessed.”