Paul teaches that God desires that all are saved, yet, in His goodness He does not impose salvation upon us. If God desires something, then it must be possible, for “all things are possible” with God.
Those unbaptised who die before reaching the age of reason are in the same broad category as those covered by “invincible ignorance” whom the church teaches “may be saved”.
The significant difference of course is that those unbaptised who reach the age of reason, ignorant of the teachings and claims of the church, may come to know Christ through His creation, and by this become members (however imperfectly) of the Body of Christ (the Catholic Church)
For those who do not reach this stage of development, we can trust that there is some other mechanisim by which they may be saved, but the nature of this mechanism remains obscure to us.
Regards Doc