Count me suspicious, slightly, that the optional rite of election may be more about a pastoral concession for the clergy rather than for children. It does highlight the relative importance of the various rites, the steps through which catechumens progress from one stage to another. If Election is optional, then the Rite of Acceptance is clearly the second-most important ritual in the catechumenate process.
Optional or not, RCIA gives a page of background information on the “Rite of Election or Enrollment of Names,” and we’ll cover each of these four sections (277-280) in turn, starting with …
277. The (optional) liturgical rite called both election and the enrollment of names may be celebrated with children of catechetical age, especially those whose catechumenate has extended over a long period of time. This celebration, which usually coincides with the beginning of Lent, marks the beginning of the period of final preparation for the sacraments of initiation, during which the children will be encouraged to follow Christ with greater generosity.
Catechumenate directors and pastors are given good guidance here. What does the rite mean by a “long period of time” do you suppose? Recalling that a catechumenate may take place over a period of years, my pastoral sense would be that if a year or more has elapsed since the Rite of Accceptance, then certainly child catechumens may be sent to Election and we can expect they will derive some benefit from it.
Even young children can understand that Lenten quality the Church hopes to see: greater generosity–that, in the context of faith.