Subject-verb-object (SVO)

Mathematics and physics are subjects.

There is no problem with matching.

Then look at the modifiers. First, modify the adverbials of verbs: never and always.

Then there is the attribute of the modified object: the harmony and advantage of the child.

There is nothing wrong with the attributive part. The advantages and disadvantages of children match the main body.

It can only be that there is something wrong with the adverbial, which has always been and should be repetitive and close in thought.