There are a few ways to say "孩子不懂礼貌" (a child doesn't know manners):

1. 孩子缺乏礼貌 (a child lacks manners)

2. 孩子不遵守社交礼仪 (a child doesn't follow social etiquette)

3. 孩子没有受到良好的教育 (a child hasn't been taught properly)

4. 孩子需要更多的教导和指导 (a child needs more guidance and instruction)