Interesting question, Sorry but I cannot see what this would contribute to your compost heap as they will not decompose/rot down. They also tend to smell if not hung up to dry for several days. Perhaps your daughter could try edging a flower bed with them as their oblong shape may lend itself to this? But perhaps they may be sharp if she fell over on them!

I think you mean to use the cuttlefish bones as a type of bonemeal. I would say that grounding 1 up and scattering it around the garden would do no harm, adding Calcium.

Too much would have a liming affect, as the cuttlefish is basically Calcium Carbonate, hence I said 1.

Edging a bed with them sounds quite a good idea to me.

THanks for all the responses.