This is so subjective. For us, MK is at least a 2 day park. AK is a 1 day, Epcot could be 2, but our kids would be bored. We're skipping DHS entirely this time. (Neither of our kiddos like ToT or RRC, and with TMM not having FP+, and Toy Story Land not being open, I anticipate a long line. My hubby and I enjoy Star Wars, but our kids are not super into it. Not doing park hoppers so there is no way I'd waste an entire day for this park.) It all really depends on how much time you have, what your park strategy is (do you anticipate a resort/hotel/pool break mid-day? are you a rope drop to fireworks kind of family?), etc., to really know if 1 or 2 days is more appropriate. My husband & I took an adults only trip in Oct and we spent 2 full days at MK and could have done more. We also spent 2 full days at AK and 1.5 days + at EPCOT. (We had park hoppers and did DHS for 4 hours and covered everything we wanted to do.) With your kids ages, it's a little tricky as the 12 year old and the 5 year old will probably have different interests, but I think MK will always be a 2 day park for our family.