Hi, Denise!
More than likely, life jackets will be provided for your children for the Port Adventures you've booked. However, not every shore excursion operator is as diligent as Disney about details. When my family and I were in Mexico on Disney Port Adventures, most all of them had thought of the potential needs and wants of families. We visited the beach hideaway of Las Caletas in Puerto Vallarta, and there was everything we could ever want for a day at the beach...including life jackets.
Yet, when we were taken to Lover's Beach in Cabo San Lucas, the boat was equipped, but the beach was bare. There were vendors there for drinks and snacks, but no life jackets. The surf was particularly rough that day, and I wished my little boys had been wearing some sort of life preserver. You can probably borrow life jackets from the ship or from the shore excursion operator. You'll just need to inquire about it once you're on the ship or on the Port Adventure. I don't think I'd waste space in your luggage, however.
Let me know if I answered your question to your satisfaction, and come back if you have more questions. Oh, and stay tuned to
Disney Cruise Line News' YouTube Channel for the videos we shot on the Mexican Riviera...I'll have lots of good info and tips for you there. Have a wonderful day and a magical vacation. Bon voyage!
Andi