Did Kartikeya teach Lord Shiva the meaning of 'Aum' (ॐ)?

 Lord Murugan, at certain period of time in cosmic evolution, took the role of “Creator” and Perfected the role and hence called Su+Brahma+ nyan.

The Famous Story Behind Swamimalai Murugan Temple

Swamimalai holds a special place in the hearts of Murugan devotees. The temple is said to have been built in early 2nd century BC by Parantaka Chola I. It is the fourth of six Aarupadaiveedu (the six most significant shrines dedicated to Murugan in Tamil Nadu) and is important because this is when and where the secret of the Pranava Mantra “Aum” was revealed.

The child Murugan reveals the meaning of the Pranava Mantra (Aum); Pranava means “cosmic sound” in Sanskrit. Hindus believe the whole universe is created from “Aum” and that everything has its origin in “Aum”. Swamimalai is closely linked to the story of how the meaning of this cosmic sound was revealed by Lord Murugan to his father, Lord Shiva.

Once Brahma, the Lord of all creation, disrespected Murugan when he was visiting Mount Kailash. Then, the ever-playful Murugan boldly asked Brahma the meaning of the Pranava Mantra “AUM”. Failing to answer the question, Brahma admitted his ignorance. Murugan knocked his forehead, and imprisoned Brahma, bringing the whole of creation to a standstill.

The demigods prayed to Lord Shiva for the release of Brahma. But Murugan insisted the imprisonment was a just punishment for Brahma's ignorance. Lord Shiva then asked Murugan whether he Himself knew the meaning of Pranava “Aum”.

Murugan said he knew its meaning, but would only explain it if Lord Shiva accepted him as a guru and listened to him as a devoted disciple. Shiva accepted the request, and the son became the teacher. He then imparted upon the father the meaning of the sacred Pranava mantra “Aum” and the divine father, proud of understanding the significance, conferred respect to Murugan for his wisdom.

You will see in the main shrine in the temple complex in Swamimalai that Murugan is depicted as a teacher and Shiva is listening as a disciple and, in this temple, the son is on a higher pedestal than the father.