I detest the idea of loyalty pledges of any kind.
It feels like a sin to make your children say these pledges before they even understand what they mean.
It is *always* compulsory when a 6 year old is told by an adult to memorize and recite this verse. The 6 year old does not have the machinery, yet, to decide whether it's something they want to do or not. Nor to stand up to a teacher, if the child decides it's not what they want to do.