My cat is scared, wht do i do?

My neice and nephew are from new york and theyre visiting for a month or two. He's 8 and she is gonna turn 7 in a month. They r very loud. My cat is used to a more chill and relaxed environment. When they come down the hall or in my room or even if theyre in the living room and r being too loud he goes under my bed, he barrely comes out to eat. Wht do i do to help relax him? Giving him to someone else to watch is totally out of the question, i trust no one with him and he doesnt like i alot or ppl. Jus me and my sisters, he doesnt even like my mom anymore. All answers will b greatly appreciated :) thanx in advance