We have three and a half days in the parks. I was planning on doing one regular morning at DL, one MM at DL, and then one regular morning at DCA. Would it be possible to go into DL at park opening (usually two hours before DCA) and do Nemo then? Then we could get FP for something and head back out to park opening at DCA?
My dd has been to WDW twice and loved the characters. She is so ready to meet the princesses (she mentions it at least once a day). How is the line at PFF set up? If we line up at park opening for PFF, could we seperate to ride a ride and still find each other? I thought maybe dh could take the kids on Buzz while I wait or something.
Ok, so here's what I would suggest...
For your one regular day at DL, I would head straight to the PFF so your DD can visit her princessess- for girls, it's totally worth it!
However your DS may be bored and a little irrated to be surrounded by all the girly stuff, I know mine would be. Maybe you could split up? You take DD to the PFF and DH take DS, maybe on Buzz and Autotopia? Frankly, these 2 rides aren't huge draws for girls your daughter's age (2, right?) and if you don't NEED to ride these 2 rides, then I would just plan on splitting up for an hour or so and then meeting back up when done.
For your MM day, don't waste it on PFF. We always use our MM day to hit the "big ticket" rides that will be swamped for most of the day after MM is over. Prior to having my son, this meant the mountains- Space, Splash, BTMM, etc. Now with DS, this means Fantasyland. Just choose to use it on what your family wants to see most. Nemo is a MM ride, so maybe hit Nemo first then whatever else your family wants to do. Even if you are able to get to Fantasyland by the official opening time (so Nemo then straight to Fantasyland) you'll still be there before folks who didn't have MM, since they are just entering and walking down Main St and you've already ridden Nemo and are in Fantasyland. Or Tomorrowland...whatever you priority is.
With 2 young kids, you MUST do Fantasyland, you just MUST!

This land gets hosed up worse then any other IMO, especially mid day- ugh! The rides are super short but the lines/ques are super long and do NOT move quickly. So plan on hitting it either 1st thing or last thing. It's pretty awesome at night!
As far as doing Nemo at park opening, grabbing a FP and then heading to DCA- you can easily do this. However park opening and the next hour or 2 after is usually one of the least busy times of the day at DL. I would seriously recommend staying in DL until at least lunchtime before heading over to DCA.
I think what's most important is to take advantage of the mornings at DL. So many people sleep in (cuz, hey! they are on vacation!) and don't arrive until 11ish, so use this valuable time to your advantage! DCA also clears out alot in the evenings since it's been my experience that most folks get in at park open, usually around 9 or 10am and then leave by 5 or 6pm to go to DL for the nightime shows. Going against the crowds will really save you time and allow you to do and see more. Maybe stay in DL until 5 or 6 and then head to DCA??