What should be done about pages from the Noble Qur’an that a two-year-old child tore and which have become difficult to repair?

If there was no negligence on your part, then there is no sin upon you. The Mushaf must be kept out of reach of children. If the Mushaf is no longer usable, it is permissible to burn it or bury it in a place far from desecration. The child is not sinful, because the pen is lifted from him.