Hi,
We stayed in the Crowne Plaza - The City, with our 2 kids last Autumn.
We were very happy with the hotel and it's location. It's not the cheapest but we didn't eat in the hotel, and the room was good for family - 2 double beds.
Also close to nice river walks and beside Blackfriars train station - we were able to take the train straight in from Luton airport. Used the left luggage to the max. which was great - arrived early and left late without having to lug our bags around the city ...Hope you have a good trip !!!