I live in Las Vegas and my neighbors are professional magicians. I have met Kevin James at their parties several times, and just went to see their show, The World’s Great Magic Show last week.
Kevin has an assistant, whose name escapes me at the moment, but the guy is a dwarf - that should give you a good hint as to how many of the tricks are created.
BTW, if anyone is coming to Las Vegas and would like to see those tricks, I strongly recommend seeing The World’s Greatest Magic Show at the Greek Isles (the old Debbie Reynolds casino near the Convention Center). The casino itself is a dump, but the theater is quite nice and the show is great (I list it on my Shows section on my website). Kids get into the show for free and adults pay about $50 or so or tickets. Nice variety of about 6-7 magicians, each performing their best tricks, so the show never gets stale and every so often, new magicians appear.