Have I committed a sin by recording a conversation I had with my in-laws, fearing that my son might blame me in the future?

If the recorded speech is not agreeable to its speakers being recorded, then doing so without their permission is forbidden, based on the Prophet's (peace be upon him) saying: "Whoever listens to the conversation of people who dislike it or flee from it, molten lead will be poured into his ear on the Day of Resurrection."

Some scholars have considered recording calls without the speaker's permission to be deceit and a betrayal of trust.

To avoid any transgression, you must commit to providing for your son, caring for him, and treating him kindly to earn his love and filial piety.

It is your right to see your son, visit him, and care for him. If you are prevented from doing so, you can raise the matter to the Sharia court.