So we know there can be changes to who will participate in the New Covenant.
The kind of change seems fundamentally different, however; while both males and females are baptized, due to the expansion of salvation to all (Gal. 3:28), there is an opposite limiting of communion to only those of age.
At any rate, I am not a paedocommunionist, but am mostly just interesting in the logic of the thing, particularly Calvin’s comment. 