Here is the word origin information they provided:
"Puerile" may call to mind qualities of youth and immaturity, but the term itself is no spring chicken. On the contrary, it's been around for more than three centuries, and its predecessors in French and Latin, the adjectives "puéril" and "puerilis," respectively, are far older. Those two terms have the same basic meaning as the English word "puerile," and they both trace to the Latin noun "puer," meaning "boy" or "child." Nowadays, "puerile" can describe the acts or utterances of an actual child, but it more often refers (usually with marked disapproval) to occurrences of childishness where adult maturity would be expected or preferred.
This very readily brings to mind a passage from Paul's letters:
When I was a child, I used to speak like a child, think like a child, reason like a child; when I became a man, I did away with childish things. (1 Corinthians 13:11)
This can directly refer to childish (or puerile) behavior but, in the lives of believers, can also refer to spiritually immature behavior. What are immature behaviors in the lives of believers? The sin that was part of our lives that G-d is purging out of our lives as He grows and matures us. It is this childish, fleshly, sinful behavior Paul speaks of.
Paul also writes earlier in 1 Corinthians:
And I, brethren, could not speak to you as to spiritual men, but as to men of flesh, as to infants in Christ. I gave you milk to drink, not solid food; for you were not yet able to receive it. Indeed, even now you are not yet able, for you are still fleshly. For since there is jealousy and strife among you, are you not fleshly, and are you not walking like mere men? (1 Corinthians 3:1-3)
And the writer of the book of Hebrews admonishes his readers:
For though by this time you ought to be teachers, you have need again for someone to teach you the elementary principles of the oracles of God, and you have come to need milk and not solid food. For everyone who partakes only of milk is not accustomed to the word of righteousness, for he is an infant. (Hebrews 5:12-13)
By the focus in the letter of Hebrews the author appears to be Jewish. The letter is directed to "Hebrews", i.e. Jews, whether Hellenistic Jews or native Israelites. To a Hebrew mind (of both the writer and the audience) was are the "elementary principles of the oracles of G-d"?
The Torah is taught to children from the time they are about 3 or 4 years old. The principles found there-in should be known to everyone except infants (as is noted in verse 13).
What are these principles? Here are some examples:
Love- You shall love the LORD your God with all your heart and with all your soul and with all your might. (Deuteronomy 6:5) You shall love your neighbor as yourself (Leviticus 19:18)
Joy- ...and you shall rejoice before the LORD your God for seven days. (Leviticus 23:40) ...and rejoice in all your undertakings in which the LORD your God has blessed you. (Deuteronomy 12:7)
Peace- The LORD lift up His countenance on you, And give you peace. (Numbers 6:26) Therefore say, 'Behold, I give him My covenant of peace... (Numbers 25:12)
Patience- The LORD, the LORD God, compassionate and gracious, slow to anger, and abounding in lovingkindness and truth; who keeps lovingkindness for thousands, who forgives iniquity, transgression and sin... (Exodus 34:6-7) The LORD is slow to anger and abundant in lovingkindness, forgiving iniquity and transgression... (Numbers 14:18)
Kindness- You shall not wrong a stranger or oppress him, for you were strangers in the land of Egypt. (Exodus 22:21) In Your lovingkindness You have led the people whom You have redeemed; In Your strength You have guided them to Your holy habitation. (Exodus 15:13)
Goodness As for you, you meant evil against me, but God meant it for good in order to bring about this present result, to preserve many people alive. (Genesis 50:20) It is a good land which the LORD our God is about to give us. (Deuteronomy 1:25)
Faithfulness ...My servant Moses, He is faithful in all My household... (Numbers 12:7) The Rock! His work is perfect, For all His ways are just; A God of faithfulness and without injustice, Righteous and upright is He. (Deuteronomy 32:4)
Gentleness If you happen to come upon a bird's nest along the way, in any tree or on the ground, with young ones or eggs, and the mother sitting on the young or on the eggs, you shall not take the mother with the young; (Deuteronomy 22:6) You shall not curse a deaf man, nor place a stumbling block before the blind, but you shall revere your God; I am the LORD. (Leviticus 19:14)
Self-control- Then he washed his face and came out; and he controlled himself... (Genesis 43:31) Now when Moses saw that the people were out of control--for Aaron had let them get out of control to be a derision among their enemies-- then Moses stood in the gate of the camp, and said, "Whoever is for the LORD, come to me!" And all the sons of Levi gathered together to him. (Exodus 32:25-26)
All the stories found in the Torah teach examples of what to do and what not to do. What is G-dly and what is not G-dly.
May we all read and grow beyond the milk of the Word and get to the meat of walking and doing as our Messiah Yeshua walked and did.
For those whom He foreknew, He also predestined to become conformed to the image of His Son, so that He would be the firstborn among many brethren... (Romans 8:29)