It’s really an urban legend that Vatican II and its emphasis on participation neglects the interior. Also in the status of “legend” or “myth” is the notion that progressive liturgists demur on the issue of silence.
37. Even in Masses with children “silence should be observed at the designated times as part of the celebration” [GIRM 23.] lest too great a place be given to external action. In their own way children are genuinely capable of reflection. They need some guidance, however, so that they will learn how, in keeping with the different moments of the Mass (for example, after the homily or after communion [See Sacred Congregation of Rites, Instr. Eucharisticum Mysterium 38.]), to recollect themselves, meditate briefly, or praise God and pray to Him in their hearts. [See GIRM 23.]
Besides this, with even greater care than in Masses with adults, the liturgical texts should be proclaimed intelligibly and unhurriedly, with the necessary pauses.
What the post-conciliar liturgy has struggled with more than liberals are the pragmatists, the people who reduce worship, especially worship with children, down to some functional level. Pragmatists still look at liturgy as primarily an obligatory exercise in rubrics: get the right things done, and get them done on time.
The DMC is absolutely correct that children are capable of significant interior lives.