A devotee cannot execute the order of anyone except the Supreme Personality of Godhead. This is the position of a devotee. Hiranyakasipu could understand that this boy (Prahlada) must have been very powerful, since the boy did not heed his orders
SB Canto 7
My son Prahlāda, you rascal, you know that when I am angry all the planets of the three worlds tremble, along with their chief rulers. By whose power has a rascal like you become so impudent that you appear fearless and overstep my power to rule you?
The relationship between a pure devotee and the Supreme Personality of Godhead is extremely relishable. A devotee never claims to be very powerful himself; instead, he fully surrenders to the lotus feet of Kṛṣṇa, being confident that in all dangerous conditions Kṛṣṇa will protect His devotee. Kṛṣṇa Himself says in Bhagavad-gītā (9.31), kaunteya pratijānīhi na me bhaktaḥ praṇaśyati: "O son of Kuntī, declare boldly that My devotee never perishes." The Lord requested Arjuna to declare this instead of declaring it Himself because sometimes Kṛṣṇa changes His view and therefore people might not believe Him. Thus Kṛṣṇa asked Arjuna to declare that a devotee of the Lord is never vanquished.
Hiraṇyakaśipu was perplexed about how his five-year-old boy could be so fearless that he did not care for the order of his very great and powerful father. A devotee cannot execute the order of anyone except the Supreme Personality of Godhead. This is the position of a devotee. Hiraṇyakaśipu could understand that this boy must have been very powerful, since the boy did not heed his orders. Hiraṇyakaśipu asked his son, kiṁ balaḥ: "How have you overcome my order? By whose strength have you done this?"