I'm not a fan of the current Sunday School set-up, and agree with a number of conclusions reached in the documentary (which I watched a few months ago).
1. Parents should be the primary religious educators in a Child's life, and the Church should focus on educating parents.
2. Fathers are especially critical in the religious education of children, as the usual trend is for mothers to handle "religious stuff" and, thus, the Church and faith are seen as only feminine, and not both masculine and feminine, from the POV of the kids. Both parents should be heavily involved, and when the child does not have both parents, a suitable person should be found to play the active role of the missing role model (aunt/uncle, family friend, etc.).
3. Strict age-based division is not beneficial to the kids education, and does not adequately meet the kids where their needs are (which we also see in secular education, where strict age division leaves some kids behind, and holds others back, in order to cater to the 60% in the middle), nor does it reflect social interaction in the real world (where we're not bunched into groups of 30 by age). At the very least we need to drop the model of separating each grade, and grouping kids into 4-year bunches (2yr-6yr, 1st grade-4th, 5th-8th, 9th-12th).
4. Christ's words about not forbidding the children to come to Him should ring true for us, also: Christ was preaching a message to adults that He wanted the kids to hear also; it was a message against age segregation. IMO, we shouldn't have Sunday School, children's choirs, "children's liturgies," etc. but One Liturgy, an education based on the family unit and the entire parish community, rooted in the liturgical life, scripture, and patristic writings, and founded on prayer.