Rabbits are especially prone to heatstroke, as in the wild they would be in their burrows.
Provide ice packs all day [2l cola bottles frozen with 10% air for expansion works well].
Hot ears are a sign of overheating – with a bowl of water wet the rabbits’ ears and nape of next thoroughly.
Put up an umbrella/sheet above the hutch to cast a shadow – don’t drape a sheet directly over it.
Electric fans can be used indoors – ENSURE the wire is out of reach.
If out of the sun, paving slabs will allow the animal to lie against a cool surface, these can also be hosed down to stay cooler.
Pink eyed rabbits cannot deal with direct sunlight well, but all rabbits MUST have shade.
Ice cubes can also be added to the water.
If there are signs of serious overheating [collapsing, panting, wet nose, lethargy strange behavior] – a hose with a sprinkler end or a watering can can be used to soak the fur in an emergency. Consult a vet ASAP.
Also – fishtanks – if it’s hotter indoors than your water – open the lid a crack to let air circulate [if you remove the lid it’d be cooler but you may lose a fish!]