The DP15 has the Dustin Pedroia fit, which gives it a slightly smaller wrist opening and finger stalls for an intermediate hand size. The RC22 is the same as the DP15, just without the smaller wrist opening and finger stalls, has a Mariner Green color scheme, and is the same pattern worn by Robinson Cano. The 1786 model refers to the color scheme. It still has the same standard A2000 design.
The 2017 Wilson A2000 Super Skin Robinson Cano 11.5" Baseball Glove: A20RB17RC22GM is most likely going to be too large of a fit for a 9 year old unless the 9 year old had pretty large hands. The Wilson A950 is an adult glove as well. I would recommend taking a look at the Wilson A1000 11.5" Baseball Glove: WTA10RB181789 as a good option for a 9 year old.
Yes, a 13 year old infielder could certainly fit into this 2017 Wilson A2000 Super Skin Robinson Cano 11.5" Baseball Glove (A20RB17RC22GM) and use it effectively!