Eucharist

At the Last Supper, on the night he was betrayed, our Savior instituted the Eucharistic sacrifice of his Body and Blood. This he did in order to perpetuate the sacrifice of the cross throughout the ages until he should come again, and so to entrust to his beloved Spouse, the Church, a memorial of his death and resurrection: a sacrament of love, a sign of unity, a bond of charity, a Paschal banquet 'in which Christ is consumed, the mind is filled with grace, and a pledge of future glory is given to us. (Catechism of the Catholic Church, 1323)

Resources on the Sacrament of Eucharist:

16 Questions about Eucharist
The Fountain of Love: How Parents Form Children for Prayerful Participation in the Eucharist
Eucharist: Food for the Mission by Pope John Paul II
First Eucharist preparation at St. Charles
How to take young children to Mass