By the process of bhakti-yoga, even a child less than five years old, or anyone of any age, can be purified. That is the special significance of bhakti-yoga
SB Canto 4
My dear boy, you also should take shelter of the Supreme Personality of Godhead, who is very kind to His devotees. Persons seeking liberation from the cycle of birth and death always take shelter of the lotus feet of the Lord in devotional service. Becoming purified by executing your allotted occupation, just situate the Supreme Personality of Godhead in your heart, and without deviating for a moment, engage always in His service.
The system of bhakti-yoga described by Queen Sunīti to her son is the standard way of God realization. Everyone can continue in his constitutional occupational duties and at the same time keep the Supreme Personality of Godhead within his heart. This was also instructed by the Lord Himself to Arjuna in Bhagavad-gītā: "Go on fighting, but keep Me within your mind." That should be the motto of every honest person seeking perfection in Kṛṣṇa consciousness. In this connection, Queen Sunīti advised her son that the Supreme Personality of Godhead is known as bhṛtya-vatsala, which indicates that He is very kind to His devotees. She said, "You came to me crying, having been insulted by your stepmother, but I am unable to do any good for you. But Kṛṣṇa is so kind to His devotees that if you go to Him, then the combined kindness of millions of mothers like me will be surpassed by His affectionate and tender dealings. When everyone else fails to mitigate one's misery, Kṛṣṇa is able to help the devotee." Queen Sunīti also stressed that the process of approaching the Supreme Personality of Godhead is not easy, but is sought after by great sages who are very advanced in spiritual realization. Queen Sunīti also indicated by her instruction that Dhruva Mahārāja was only a small child, five years old, and it was not possible for him to purify himself by the way of karma-kāṇḍa. But by the process of bhakti-yoga, even a child less than five years old, or anyone of any age, can be purified. That is the special significance of bhakti-yoga. Therefore she advised him not to accept worship of the demigods or any other process, but simply to take to the Supreme Personality of Godhead, and the result would be all perfection. As soon as one places the Supreme Personality of Godhead within one's heart, everything becomes easy and successful.