Our worship has been crafted by the Holy Spirit to touch all who come- including those with developmental disabilities whose intellectual capabilities are limited to concrete thinking (and have trouble with abstract reasoning) as well as those who lack certain senses.
Alongside the rich theology of our liturgy there are concrete actions, music, fragrance, icons, and more. There are words relating to everyday life and words that carry one through the Incarnate Christ into the ineffable heavenlies. The Holy Spirit can address the heart through all, or some, or even just one of these modes. The symbols of Orthodox worship- lighting candles, making the sign of the cross, kissing icons, prostration, and the like are enacted by all.
The “spiritual sensuality” of our Divine Liturgy offers mentally retarded persons much to respond to: there is repetition, concreteness, physical contact; the staples of their unique pedagogy (method of learning) inhabits the services.
See http://oca.org/resource-handbook/parishdevelopment/the-handicapped-and-orthodox-worship & http://oca.org/resource-handbook/parishdevelopment/some-practical-suggestions-for-parish-ministry-to-people-with-special-needs by Father Stephen Plumlee
Even if persons with developmental disability lack the potential to ever reason abstractly, their experience of the Mysteries (the Sacraments) can be just as rich as those who can reach that stage. For the Mysteries have Divine depth, and always beckon one forward to greater participation and fuller comprehension of their import. For the experience ultimately transcends conceptualization.
Father John Breck, in “Down Syndrome at Pascha,” in his book God With Us: Critical Issues in Christian Life and Faith, describes Marie, a woman who had Down Syndrome, at the Holy Friday service: (pp. 66-67)
She was entirely dressed in black. Her face was streaked with tears, her head was bowed, and her arms hung down at her sides. As she approached the shroud, she slowly made the sign of the cross three times, prostrated herself before it, and for a moment kept her head to the floor. Then she rose, kissed the face and then the feet of Christ, and finally venerated the Bible and the Cross.
See also Children with Special Needs and the Orthodox Christian Family , by Father Steven P. Tsichlis