Welcome aboard, Ann!
You and your little Princess will be in for such a treat once you set sail with Captain Mickey and his crew. There's so much to see and do onboard, that you might not want to leave... I never do!
Visiting Atlantis is quite convenient, especially if you book your port adventure with Disney Cruise Line. I'm assuming you're looking at the
Atlantis Beach Day & Discover Atlantis adventure. Your excursion will be handled with loads of care and you can even have a choice of a half day or a full day. My family and I did the full day and we had fun exploring Atlantis with our kids. You'll have a quick ride in a shuttle through the town, then you'll be dropped off at the resort.
Just be warned, your 2-year old might not want to walk too much and she may ask to be carried around. If you travel in the warmer months - this can take a toll on mom and dad. You might want to plan on bringing a light umbrella stroller... it'll be perfect when she naps on your way back to the ship :-). Atlantis is a good sized resort and there's lots of exploring that you can do. My kids enjoyed checking out the many sea friends that live there and we burned a lot of energy at the beach and pool area. You are allowed to use the changing areas there, as well as the beach chairs, loungers and umbrellas.
On your way back to the ship, you'll be walking back from the resort to the shuttle pick up area - it's about a 10-15 minute walk, depending on how fast you go. Since your little one might be exhausted after playing in the water and exploring the grounds, she'll likely be napping on your walk back to the shuttle pick up area.
I hope this information helps, Ann. Let us know if you have any additional questions.
Happy planning,
~ Dolly