Can imagining disgusting things and people's private parts, and imagining children being tortured, and many negative things have an effect?

A person is not held accountable for the thoughts and imaginations that occur within him. However, guarding one's thoughts is important for fortifying the heart and protecting the limbs. Therefore, you must strive to repel these thoughts by occupying yourself with virtuous deeds, and your heart with contemplating what benefits you in your religion and your worldly life, and with Allah's names and attributes, and with the terrors of the Hereafter.