Hi Kellie,
Welcome to the Moms Panel, and congratulations on planning your first cruise! The dining themes will loosely follow those of the 4-night voyages. You'll have a mix of cruise casual, Pirate (optional), and one formal/dress up evening.
Now you'll see widespread variations on what guests consider "formal" (I think they actually classify the evening as "Optional Dress Up"). There will be a few tuxedos and evening gowns, but it certainly will not be the norm. I am a firm believer that it isn't necessarily what style you wear, but how you wear it. I think you can clean up nicely in a pair of slacks and a polo shirt, belt, shoes - and look just as good as someone that pulled out a rumpled suit from years past.
For my family, I would have the girls in dresses, and my son would be in chinos and a collar or oxford shirt. As for me, I still try to keep it simple. Typically I'll wear nice dress capris and a fancy top, I rarely wear dresses. My husband prefers the chinos and oxford route.
Keep in mind that if you have plans on dining at
Palo, a dress shirt or jacket is recommended for men and a dress or pantsuit is for women.
I hope this helps!