SMS Tracker is a free Android app for intercepting a child's text messages. As of April 2015, there is no equivalent app for iPhones; all iPhone solutions require logging into the child's Apple account from another device.
Message interception apps such as SMS Tracker are not legal in all states – even when a parent uses them for a minor child's phone. Users should consult local laws before utilizing any app or service that intercepts text messages and never intercept messages for any adult children. Reading or intercepting text messages is a violation of federal wiretapping law, and there are no state exemptions for spying on the electronic communications of an adult.