I think that parents are the best teachers to the children is not always accurate because parents sometimes will do some negative effect to their children.
正确.
从that到children（句末）部分整个为think的宾语.
从parents到children（句中）部分是宾语从句中的主语从句.
从because到children（句末）是宾语从句中的原因状语从句.