Unable to kill sound alert and have a banner pop up.. Which would also make iPad unusable to child, so you will have to be involved in shutting off alarm. Any child can/will figure out that you only need to take a few seconds to turn off and on device to disable this app and continue using iPad.
Save yourselves $1, use the timer/alarm that comes on the iPad and have consequences if they do not put it down this app does little more than that.
EpicAdam1166 about Playtime Timer