Is the act of fondling and kissing by a boy who has not reached puberty towards a girl, without penetration or sight of 'awrah (intimate parts) except for the breasts, considered zina (unlawful sexual intercourse) and subject to its rulings?

The boy is not held accountable, as the pen has been lifted from him. Therefore, he is not censured for what emanated from him before puberty, such as looking at or touching non-mahram (definition) women, based on the Prophet, peace and blessings be upon him, saying: "The pen has been lifted from three: from the insane person until he recovers, from the sleeper until he wakes up, and from the boy until he reaches puberty."

After reaching puberty, it is incumbent upon him to be righteous, to distance himself from thoughts that remind him of his past, and to hasten to marry. If marriage is not possible, he must fast frequently.

What was mentioned in the question, if it occurred from an adult, is not considered zina (fornication/adultery) in the specific sense that incurs the prescribed punishment. However, it is zina in the general sense, based on the Prophet, peace and blessings be upon him, saying: "Indeed, Allah has ordained for the son of Adam his share of zina, which he will inevitably attain. The zina of the eye is looking, the zina of the tongue is speaking, and the self wishes and desires, and the private part confirms or denies it."