This shows an example of registering circular types in WPGraphQL v0.3.2

register-circular-types-in-wpgraphql.php

add_action( 'graphql_register_types', function() {

	$myCustomType = [
		'someField'    => 'Some value...',
	];

	register_graphql_object_type( 'MyCustomType', [
		'fields' => [
			'someField' => [
				'type'    => 'string',
			],
			'child'     => [
				'type'    => 'MyCustomType',
				'resolve' => function() use ( $myCustomType ) {
					return $myCustomType;
				}
			],
		]
	] );
	register_graphql_field( 'RootQuery', 'myCustomType', [
		'type' => 'MyCustomType',
		'resolve' => function() use ( $myCustomType ) {
			return $myCustomType;
		}

	]);
});