An aquarium fascinates children precisely because it is alive, glowing and full of water, and it sits in the home as three hazards at once: a heavy glass box, a body of water, and mains electricity running into that water. Childproofing means working through each of the three in turn, before the first small visitor presses a nose to the glass.
Keep Hands and Objects Out of the Water
Fit a proper lid and keep it closed, clipped down if the rim allows clips, so that hands, toys and dropped snacks stay out and fish stay in. A determined toddler should not be able to slide it open. Feed through the lid's hatch yourself rather than leaving food where a child can help — overfeeding by a generous small hand is the commonest aquarium accident in family homes, and the fish suffer for kindness. Keep nets, scrapers and test kits in the same locked place as the food rather than in an open bucket beside the stand.
Lock Away Everything in the Cabinet
The cabinet under a tank is a low cupboard at exactly toddler height, and it typically holds water treatments, fish foods, spare equipment and cleaning chemicals from around the home. Fit a child lock or latch to the doors and treat the contents as you would medicines: interesting, unlabelled to a child, and not for tasting. Bottles kept capped and upright inside a locked cabinet — that is the whole system — it only fails when someone leaves the door ajar after a water change, so make shutting and latching it part of the routine's last step.
Make the Electrics Boring and Untouchable
Every cable leaving the tank should dip into a drip loop — a sag in the cable below the socket, so water tracking along it drips off the bottom of the loop instead of running into the plug. Run the equipment from a socket protected by a residual-current device, keep the plug strip itself raised inside the cabinet rather than lying on the floor where a spill can reach it, and gather cables into trunking or ties so there is nothing dangling to pull. A child hauling on a heater cable can drag equipment off the stand; trunking removes the handle. If your home's sockets are not protected, an electrician fitting protection on that circuit is money well spent.
Settle the Stand and the House Rules
A tall stand a child can climb or swing on should be anchored to the wall behind it, and step stools and chairs should live away from the tank so nobody gains a climbing route to the lid. Then agree the rules and keep them few and kind: we look with our eyes, we never tap the glass, feeding is a grown-up job that children can watch and count. Children rise to being trusted with a ritual; watching the evening feed becomes the treat that replaces touching.
Write those few rules and the cabinet-and-electrics arrangement down once, where grandparents, babysitters and older siblings will actually see them. KinsLe Family Sharing gives relatives you pick access to its profile, for a relative supervising the tank room.