Vine Weevil Grubs in Raised Beds
In answer to your question, yes 'Nemasys Vine Weevil Killer' would be a safe alternative to chemicals to use in your garden. The nematodes (Steinernema kraussei) supplied in this pack https://www.harrodhorticultural.com/nemasys-vine-weevil-killer-pid7624.html are harmless to us, and animals when used properly. These nematodes do occur naturally in most soils but in low numbers, so by applying many thousands in an infested area increases the chances of one coming into contact with the unwanted Vine Weevil larvae. Follow the application and safety guidelines included and you can't go wrong. As with most bio-controls use sensibly around children i.e. don't let the children eat and / or drink them, put them in their ears or up noses!
I would apply the nematode solution after the children have gone home for the day or weekend, and so giving them plenty of time to soak into the soil overnight and get to work on the larvae undisturbed.
It sounds like a great job your doing with the children Sue and its great to get them interested in and exploring the garden at such a young age!
I hope you don't mind but I've taken the liberty to attach this shortcut http://www.buddinggardeners.co.uk/ Harrod Horticulturals 'Budding Gardeners', its a few pages on their website aimed at schools, children's centres and young gardeners alike. It contains some offers and seasonal fun things to do! Thought you might find it of some interest.
Many thanks for your query.