Hi LOUPINK,
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Disneyland Paris Trip Planning & Community Board

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Both hotels are fine to stay in, it really depends what you want from your hotel

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The Dream Castle is better, in my opinion, for couples, or families with older children. The reason I'm saying this is the room furnishings are nicer, the bathrooms are bigger with premium brand toiletries etc, and the breakfast includes hot items free of charge.
If you have young children, in my opinion the Explorers is the way to go, it has a fabulous themed swimming pool with one whole corner of it dedicated to a water-play pirate ship, plus it has a large indoor soft-play area.
The location is the same for both, and they are both served by the same free shuttle bus to and from the parks.
You don't get hot items at breakfast at the Explorers unless you pay extra for it, and you aren't seated by a waiter in the restaurant at breakfast at the Explorers (you are at the Dream Castle and Magic Circus).