"No, it is the Sunday school teacher who will decide when the children can be presented to the priests as prepared to take the sacrament."
My God, that's even worse! As for denying the Eucharist to persons who have not been received into the Church, that's the way it has always been in The Church, with reason. I am assuming, however, that the children with mental retardation who are denied communion simply because, I guess, some lay Sunday School teacher doesn't think they are "ready", are baptized members of The Church and far more likely to be in a "state of grace" than their non-retarded fellows.
Infants do not take communion, neither do any children in the parish who have not received the appropriate instruction about what they are receiving. I support the teacher's optimism about achieving a spiritual awareness of the meaning of the eucharist in my son and her track record of providing appropriate religious education to handicapped kids, including teaching an autistic child under the table for two years before the child was able to be part of the communion service. If I did not, I could take my kids to the Methodist church and let them line up for bread and grape juice with absolutely no awareness of why.
Good luck to you in your own beliefs and church of choice.