The main difference between this 2017 Marucci Hex Connect -8 Senior League Baseball Bat: MSBHCX8 and the 2017 Marucci CAT 7 Senior League Baseball Bat: MSBYC78 is that the Connect is a multi-piece fully composite bat while the Cat 7 is a one-piece alloy model. The Connect will be more comfortable on contact, but require a break-in period before reaching a peak performance threshold. Both are held to the same USSSA standards and therefore there really will not be a noticeable performance difference between the two.
Our sizing chart has your 12 year old right at the 32'' for his size in the 2017 Marucci Hex Connect -8 Senior League Baseball Bat: MSBHCX8. It would be a great bat for 13 and under for your son.
Whether or not to move up in size on the 2017 Marucci Hex Connect -8 Senior League Baseball Bat: MSBHCX8 for your 11U player would ultimately come down to whether you feel your son's bat speed will be negatively impacted by the added weight. Generally, a player of that age would benefit more from a -10 model but if you feel he can handle an additional 2-3 ounces then there is nothing wrong with going that route.