In Child Guidance, beginning on page 486 is a chapter entitled, "Leading Little Children to Christ." The instruction here indicates that even small children may understand what it means to have their sins forgiven and to be accepted as members of God's family, even though they do not understand the doctrines. I think the same would be true of these mentally defected or retarded children. And surely it is a worthwhile task to endeavor to help them to know and love Christ.