These may be of leather, plastic, lace, etc. People with a paraphilia for nonhuman objects often masturbate while holding, rubbing or smelling the article. They may ask their partner to wear the article while having sexual contact with them. Usually the article is required for sexual arousal. Often, if the article is not present, it is difficult or impossible to maintain an erection.
Some sadists find partners who are consensual which means they have agreed to be the partner.
Some sadists do not care about finding partners who agree. Most pedophiles have specific age children that they are attracted to and often prefer one sex or the other. Some prefer to just watch the child undress and may masturbate during this, others actually touch the child. Some may use force to penetrate the child in whatever way sexually excites them. Frotteurism is touching or rubbing up against another person.