By Alyson Krueger, The New York Times Company Kiley DeMarco recently attended Safety Night at her children’s public elementary school on Long Island in New York. As she walked around different booths learning about how to protect her children from accidentally taking a cannabis gummy, about a local violence-prevention program, about how police officers would respond to an emergency on campus, one station caught her eye: A parent was asking other parents to take a pledge not to give their children smartphones until the end of eighth grade. DeMarco has two children, one in kindergarten and one in first grade.