Will be staying with GPs who live near Dover in the summer. DC (4 and 2) have never been abroad (or on a boat at all) so thinking of popping over to Boulognr for a day trip, but are they too little? Is it explorable on foot without having to walk miles? Where's good to run about outside? What if it rains?? And does the ferry even go direct to Boulogne. And have I left it too late to get passports??