Is masturbation before puberty forbidden? And is engaging in sexual intercourse before puberty forbidden if the opportunity arises?

You have reached the age of religious accountability (taklif) by the emission of semen from you. This makes masturbation, fornication, and other acts forbidden for you. You must repent immediately and adhere to the law of Allah by keeping company with the righteous and making supplication. For the emission of semen, in whatever manner it occurs, signifies puberty by the consensus of Muslims.