Block booting into safe mode

I am using a porn blocker to protect my kids. But I got to know that there is a workaround to that by rebooting into safe mode. I also tested it and I was able to access everything. Now my paid subscription to blocker seems useless. I am also worried about the kids. So is there any way I can block safe mode in my device? Like editing build.prop file or making any other change and safe mode blocker.