That depends if the lava lamps are in the public domain or not.
I use You tube on my site, but i won't sue another site that uses it too, because You Tube is universally available to anyone. Check out the lava lamps and read their conditions for use, If they are available for download or use by anyone then the "Other" site, hasn't got a leg to stand on.
At 13 and 14, i doublt that they could mount a legal challenge and inccur all the legals cost prior to going to court.
Try not to let it worry you but check out about the lamps if they are copyright free, use them
Well, the lamps are made by Ganz, and on their website they say
"The Lava Lamps are made by Ganz, and we do not own them" or something like that, so I don't think that. And really, anyone with a Webkinz account could just take a screenshot of one..