I overexpose my color neg stuff by up to 1 stop. In Utah, in the afternoon the sky is going to look washed out the closer to noon you are. If you want to saturate the colors go for the light between 4 and sundown. Since you are shooting your kids a polarizer is going to slow you down by two stops. If your kids are like mine, 2 stops lost will make you lose a few shots because the little boogers are moving too fast.
Are your skys washed out and kind of dull? If so shooting in the later afternoon should make them look better. You could also shoot the Portra VC to punch things up.