I find frozen grapes helpful! They're a sweet, cooling treat that can double as a healthy snack. Wash and dry grapes, then freeze them in a single layer on a tray before transferring to a storage container - they satisfy my sweet tooth no end!
Also, chill soups are great; gazpacho is a fantastic option and so easy to blend together - just throw in some tomatoes, peppers, cucumbers, onions and garlic for a refreshing, savoury hit. Cold pasta salads with loads of veggies work well too, and you can make them interesting by switching up the herbs and dressings. For fussy eaters, I've had success with making fun shapes with their food - think vegetables cut into stars or hearts, or using cookie cutters to shape sandwiches. Sometimes, presentation makes all the difference!