The best free day out on the British coast

Few things hold a child's attention like a shallow pool of seawater with something moving in it. Rock pooling costs nothing, works on almost any rocky shore around the UK, and offers the rare combination of fresh air, genuine discovery and complete absorption. Give a six-year-old a net and a magnifying glass and an hour will vanish without a single complaint about being bored.

Our coastline is exceptionally good for it. Cool, nutrient-rich seas mean British rock pools are crowded with life, and because the tide goes out twice a day, the whole exhibition is free and open to anyone with wellies. What follows is everything you need to know to make a trip work — practically, safely and kindly.

Timing your visit around the tide

Everything depends on the tide. Check tide tables for your chosen beach the day before you go, and aim to arrive about an hour before low water. That gives you the longest safe window and the widest stretch of exposed shore. Two hours either side of low tide is the sweet spot; after that, the water starts reclaiming the gullies you are standing in.

Spring tides — the biggest of the month, falling around the new and full moon — pull the sea back furthest and expose the richest lower-shore pools. Neap tides leave far less on show. If you only get one trip, pick a spring low.

Most important of all: never turn your back on the sea for long. Rocky headlands and wide flats can cut you off faster than you expect, and the water often returns around a headland before it reaches you from the front. Keep an eye on the water's edge, and if it is creeping in behind you, move.

What to pack

• A small net with soft mesh — the sort sold for aquariums. Rigid frames scrape rock and damage the animals you are trying to catch.
• A white-bottomed tray or a clean margarine tub. A pale base makes tiny, transparent creatures visible.
• A magnifying glass or a small hand lens, which turns a boring brown blob into something extraordinary.
• Wellies with proper grip, or old trainers you do not mind soaking. Wet rock covered in green seaweed is genuinely slippery.
• Warm layers, a towel and a full change of clothes per child. Someone will sit down in a pool.
• Sun cream and a hat. A rocky shore reflects a surprising amount of light, even on a breezy day.
• A basic first aid kit: plasters, antiseptic wipes and something for grazes. Barnacles and limpets are sharp.
• Wet wipes or hand gel for afterwards.

Leave behind glass jars, spades used for levering up boulders, and any plan to take living creatures home. Almost nothing survives a bucket on a windowsill.

Where the best pools hide

You do not need a famous beach. Any rocky shore with a decent tidal range will do, but the best pools tend to sit low on the shore, closest to the low water mark, where they are submerged for longest and stay coolest. Look for sheltered hollows fringed with seaweed, and for narrow gullies between rocks where water drains slowly rather than rushing away.

Chalk shores, slate in the south-west and the granite and basalt of Scotland and the north each offer something different, but the technique is the same everywhere: work slowly along the edge of a pool, then peer in rather than plunging a net straight into the middle. The richest spots are often under the overhang of a large, firmly settled boulder — never try to move those, both for your safety and because they are the local equivalent of a tower block.

Gentle hands: how to look without harming

Rock pooling is at its best when children learn that they are visitors. Wet your hands before touching anything, because dry skin damages the delicate surfaces of anemones and soft-bodied creatures. Never prise a limpet off a rock; they clamp down hard and you will injure them trying.

If you lift a smaller stone, put it back exactly as you found it, dark side down, so the algae and animals underneath are not left exposed to the sun. Keep anything you catch in the tray for no more than twenty minutes, in the shade, and put it back precisely where it came from. Anemones, crabs and snails all have their own patch and rarely thrive when moved.

Staying safe, and what you might find

Before you go, tell someone where you are heading and roughly when you will be back. Carry a phone, though signal on remote shores can be patchy, and be wary of deep gullies, sudden swells and anything sharp underfoot. Watch children closely on wet, weed-covered rock and keep them away from the very edge.

As for the reward, expect to meet common shore crabs scuttling sideways under stones, hermit crabs in borrowed shells, and beadlet anemones glowing red like little jellies when open. Limpets and periwinkles carpet the rock, dog whelks and topshells hunt among them, and barnacles and mussels cluster where the waves hit hardest. If you are patient, you may spot a blenny darting between weed fronds or a prawn hovering in the shadows. Take a photograph, name a few things together, then let everything go.