In Europe, our kids enjoyed fairly low-profile holidays when they were toddlers. We mostly did self-catering renting chalets/apartments in Switzerland and Germany near Bodensee. Activities are riding kiddie bike, kiddie hike, cable car rides, pick your own farms, pony rides, local children's playground, swimming pools and lake shores. Minorca villas are nice esp if you can avoid real peak season (too hot/too crowded/too expensive), but you do need to inquire if the swimming pool has a gate/cover. Cottage holiday in Jersey or Cornwall is another idea though weather is not guaranteed. Not a big fan of activity camps/leisure parks.