Some useful perspectives, including the notion that the DMC is a supplement to the GIRM:
4. All the details of Eucharistic celebration with a congregation were determined in the General Instruction of the revised Roman Missal published in 1969. Then this Congregation began to prepare a special Directory for Masses with Children, as a supplement to the General Instruction. This was done in response to repeated petitions from the entire Catholic world and with the cooperation of men and women specialists from almost every nation.
Local and national adaptations are provided for:
5. Like the General Instruction of the Roman Missal, this Directory reserves some adaptations to the conferences of bishops or to individual bishops. [See nos. 19, 32, 33 of this Directory.]
And national conferences may petition the CDWDS for what is “necessary” in a given nation:
Some adaptations of the Mass may be necessary for children in a given country but cannot be included in a general directory. In accord with the Constitution on the Liturgy art. 40, the conferences of bishops are to propose such adaptations to the Apostolic See for introduction into the liturgy with its consent.