Hi Catherine,
This is the lava lamp link (https://spark.iop.org/lava-lamp), it is suggested for 11+, but I agree that it can be used by younger children as it is very similar to Dancing Raisins from Curious Minds:
https://www.sfi.ie/site-files/primary-science/media/pdfs/col/dancing_raisins.pdf
I think there could be really interesting discussions about the behaviour of the peanuts vs the raisins, do they both rise? which one is faster? is the speed related to the number of bubbles? size of bubbles etc.
From these observations (which could be in the ‘explore’ part of the inquiry framework) children can then ‘go deeper’ with a slightly different set up to verify their understanding.