SB 4.10.1
maitreya uvaca
prajapater duhitaram
sisumarasya vai dhruvah
upayeme bhramim nama
tat-sutau kalpa-vatsarau
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The great sage Maitreya said: My dear Vidura, thereafter Dhruva Maharaja married the daughter of Prajapati Sisumara, whose name was Bhrami, and two sons named Kalpa and Vatsara were born of her.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
It appears that Dhruva Maharaja married after being installed on the throne of his father and after the departure of his father to the forest for self-realization. It is very important to note in this connection that since Maharaja Uttanapada was greatly affectionate towards his son, and since it is the duty of a father to get his sons and daughters married as quickly as possible, why did he not get his son married before he left home? The answer is that Maharaja Uttanapada was a rajarsi, saintly king. Although he was busy in his political affairs and duties of government management, he was very anxious for self-realization. Therefore as soon as his son Dhruva Maharaja was quite worthy to take charge of the government, he took this opportunity to leave home, just like his son, who, without fear, left home for self-realization, even at the age of five years. These are rare instances from which we can see that the importance of spiritual realization is above all other important work. Maharaja Uttanapada knew very well that to get his son Dhruva Maharaja married was not so important that it should take preference to his going away to the forest for self-realization.