Hi, Carrie! Each of these longhouses is close to the Great Ceremonial House, pools, and monorail. They would each be great choices, but I have one small caution. Niue is the smallest longhouse at the Polynesian, and there is no elevator in the building. There, however, is a second floor walkway to Rarotonga which has an elevator. I only mention this because sometimes, at the end of a long, fun day, everyone is tired. Babies sleeping in strollers do not like to be awaken because they have to be carried, so having an elevator option is nice.
Whether to pick a garden or lagoon-view room is a very subjective question. I bet the Moms Panelists would answer this one fifty-fifty. I would choose a lagoon-view room. Most lagoon-view rooms feature great views of the Wishes Nighttime Spectacular, the Magic Kingdom fireworks . If you prefer a garden-view room, with its normally quieter setting, any place on the Polynesian beaches or boat dock offer good places to watch the fireworks when it's time. Also be sure to catch the Electric Water Pageant as it floats by the Polynesian each night at approximately 9:00 P.M. Happy planning and have a Magical vacation!