The enclosure looks great, I am sure your little ones will love it. Is the fake grass removable, i use astro turf so i can take it out, sterilize it and hose it off. I asked the same question about the paint (see 'paint good or bad) and I was told to use either kids art paint with a pvc sealer or a low fume paint without lead. I would guess that you can use any of the silicons that you would use on a fish tank to seal large holes, if its not going to affect the fish tank water it should be OK. good luck.