The sentence "子供達が母を幸せにするのが、自然の原理。" translates to "It is a natural principle that children make their mother happy." Let's break down the grammar points in this sentence:
子供達 (こどもたち) - "children" (plural form of "子供 (こども)" meaning "child").
が - Subject marker. It indicates that "子供達" is the subject of the sentence.
母 (はは) - "mother."
を - Object marker. It indicates that "母" is the direct object of the verb "する."
幸せにする (しあわせにする) - "to make happy." This is a verb phrase where "幸せ (しあわせ)" means "happiness," and "する" means "to do" or "to make."
のが - This is a nominalizer and subject marker combination. "の" turns the preceding clause ("子供達が母を幸せにする") into a noun phrase, and "が" marks it as the subject of the main clause.
自然の原理 (しぜんのげんり) - "natural principle." Here, "自然 (しぜん)" means "nature" or "natural," and "原理 (げんり)" means "principle."
In summary, the sentence structure can be broken down as follows:
子供達が母を幸せにするの (The fact that children make their mother happy)
が、 (is)
自然の原理 (a natural principle).