Google app (now?) widget and new app installation

Hello to all, I'm new to the norton family and have some questions, which I couldn't clarify with help sites or community forum. First of all: installing of the new apps - How can I as device admin (or do google call it Owner?) prohibit new apps to be installed by my child? Second: I have configured the usage time, device can be used. Still, even if the time is up, some apps can be used. Google now (widget?) which can be accessed from the home screen, the search is working, you could search for text, images and so on.. as it seems preview of the pictures is completely sufficient for the child to be occupied for hours. That is NOT the intention of the time lock IMHO. The idea is to put the device away and go live the live full of everything else than the little phone reality... where can I find solutions? Somebody help?