I am giving birth to my second child soon, in sha Allah, and my firstborn will turn 2 years old shortly after. I had already weaned him, but he still asks for it sometimes. I think when he sees me breastfeeding, he will want too. Is it permissible to breastfeed after the second year of life?

The complete term of nursing is two years, for Allah Jalla wa ʿAlā says, the meaning of which is, the mothers nurse their children two complete years, for whoever wishes to complete the nursing (Sūrat al-Baqarah, ayah 233). Nursing a little beyond the two years is permissible when there is a need, for example if the child still turns to it and does not yet manage with food, so there is no harm in nursing him until he is content with eating. Keep in mind only that nursing after the completed two years does not establish the foster ties of maḥramiyyah, it is simply nourishment for the child. I do not advise making him go back to breastfeeding, but this is not a religious ruling, just my recommendation.