Styrofoam melts really easily. Hot glue would melt it (I've tried). E 6000 works great, but smells awful. Silicon really is the best way to go both for animal safety and adhesive properties.
if you watch all the videos it will say the size think they were 3mm x 20mm neodithium magnets please watch other videos as I have mentioned it in another. Sorry but it was a few years ago when I made these.