Does anyone believe that Baptism of Desire can apply to infants who have yet to reach the age of reason? Or do you only believe in Baptism of desire for adults who have reached the age of reason?

Isn't the teaching on BOD only applicable to those who are catechumens?  Infants and children wouldn't apply in that scenario.

Baptism of desire doesn't only apply to catechumens.

For example, someone invincibly ignorant of the Catholic faith who has perfect contrition for their sins and desires to fulfill all the precepts of God fulfills the condition of desiring and intending to receive, implicitly, the baptism of water.

Pope Pius IX (19th century): Encyclical of Pope Pius IX, Quanto Conficiamur Moerore 1863: “There are, of course, those who are struggling with invincible ignorance about our most holy religion. Sincerely observing the natural law and its precepts inscribed by God on all hearts and ready to obey God, they live honest lives and are able to attain eternal life by the efficacious virtue of divine light and grace. Because God knows, searches and clearly understands the minds, hearts, thoughts, and nature of all, his supreme kindness and clemency do not permit anyone at all who is not guilty of deliberate sin to suffer eternal punishments.”