We are bringing our two children (ages 12 and 15) to London for the first time in mid June. We have rented a mews house in Belgravia for the first week and have two additional nights before we return to the US. We aren't sure whether to just book into a hotel in London for those nights or to try to get out of town. We'd love to try a country house hotel but are concerned about getting to Heathrow for our return flight on Monday morning(we need to be there by 11am). We are planning day trips to Stratford-upon-Avon, Bath and Stonehenge. Any suggestions of what we could reasonably do with this time?