In the printer’s manuscript, Oliver Cowdery initially wrote repentance, which he immediately corrected by crossing out the word and supralinearly inserting baptism (as well as the following verb denieth). As explained earlier in Mormon’s discourse, little children need neither repentance nor baptism:
Since either word will work here in Moroni 8:20, the immediate correction, baptism, undoubtedly follows the reading of the original manuscript. Note also the occurrence of baptism alone, also in this chapter:
This reading strongly supports the occurrence of baptism later on (namely, here in Moroni 8:20).
Summary: Maintain in Moroni 8:20 Oliver Cowdery’s corrected reading in 𝓟 where baptism replaces repentance; either word is theoretically possible in this context, so Oliver’s correction very likely follows the reading in 𝓞.