The kids were blaring on the playground, so the teacher had to stop them.

blaring 是动词 blare 的现在分词形式。blare 的意思是"发出响亮刺耳的声音"，常用来形容喇叭、音乐或人声等噪音。在这里指孩子们在操场上大声喧哗吵闹。