The kids were burbling excitedly, but no one could understand what they were saying.

burbling 是动词 burble 的现在分词形式。burble 的意思是"发出咕噜声"或"兴奋地说话"，常用来形容孩子或水流发出的连续不断、含糊不清的声音。这里用来描述孩子们兴奋地说话但听不清楚的状态。