Having taken the kids to London and Paris last year, we found very poor value in Hyatt properties (although Hotel du Louvre was closed). We ended up staying at Holiday Inn Mayfair (next to Green Park Underground station and across the park from Buckingham Palace) on a cash rate, and at a boutique hotel in Paris. Unless you need qualifying nights, there are better and cheaper options in those cities, especially if you need a room that sleeps 4, and want breakfast included in the rate.