SELECT
    osm_lakes.osm_id,
    osm_lakes.name
FROM
    multipolygons osm_lakes,
    (
        SELECT osm_polygon.way
        FROM multipolygons osm_polygon
        WHERE osm_polygon.name = 'Manchester'
    ) cities
WHERE
    osm_lakes.leisure = 'playground' AND
    ST_WITHIN(osm_lakes.way, cities.way) = TRUE