As the original people who asked about visiting Calis in April have already booked, it really doesn't matter about our opinions. Lets wait and see what they think when they come back. Its clear that it will be quieter and cooler than in the summer months, but will give them the chance to explore the area and make their own decisions as to future visits. As they are tied to school holidays at this time of their lives and the summer months are too hot (and expensive) April is Calis is better than the UK even if its not all "open".