It's another of the many ideas in his book The Dangerous Book for Grandads aimed at grandparents, parents and children alike and encouraging excitement, wonder and collaboration.
In this particular section he continues.
'Originally, the expression ‘beachcomber’ came from a description of someone who actually earned a living by ‘combing’ the seashore in search of things to sell and trade but, nowadays, the term can be applied to anybody who walks along the beach looking for anything interesting. What you are likely to find depends to some extent on the time of year; the storms of autumn and winter, for example, throw plenty of objects onto the seashore – ranging from crustaceans from the seabed to long ago discarded milk bottles and rusty tin-cans.
If the shore runs beneath a cliff made of soft rock or clay where the constant pounding of the waves at high tide have caused landslides and rock-falls, you might be lucky enough to discover some pieces of rock that contain fossils of ammonites (the relatives of modern-day two-shelled molluscs). If you are in an area known for fossils (the Jurassic Coast of south-west England, for instance), it could prove very worthwhile to split open any likely-looking small pieces of rock with the aid of a fossil hammer.
nb: Bear safety in mind if you go fossil collecting along cliff bottoms and in old disused quarries – and wear protective safety glasses when chipping away at rocks so as to prevent splinters flying into your eyes.
Craft a scary dinosaur from flotsam and jetsam
If you don’t find a genuine dinosaur out fossil-collecting – and it must be admitted that we’re not seriously suggesting you might! – then, rather than risk boredom setting in, combine beachcombing and fossil-hunting in order to build a pretend one out of any and every bit of available flotsam and jetsam, or out of piles of sand and pointy-shaped rocks. And if you can’t even get to the beach, try fossil-hunting closer to home or have a dinosaur rally by making ‘hobby-saurs’ (like a broomstick hobby-horse, only scarier and with lots of teeth!) and giving a prize for the best/scariest one.'