I'd go for fresh produce instead of specifically fruit. If they will eat smoothies/juice, that's better than nothing for now! Just keep it natural and not artificially sweetened. Fruit can seem kind of labour-intensive; think of preparing a pineapple or mango or even an orange.
Try snacky finger foods like berries, cherries, grapes, baby carrots, mini cucumbers, little peppers, broccoli and cauliflower florets, orange or tangerine segments, edamame, cherry tomatos. Mine will dip almost any raw veggie in hummus. Fruit leather and dried fruit can be good as a portable snack. Mashed banana and mashed avocado could appeal.
Fruit can go in/with other things: cereal, granola, muesli, porridge, yoghourt, ice cream, even in a salad.
If there's a outdoor or farmers' market near you, go as a family trip on the weekend. Browse and talk with the vendors, and then everyone picks what fruit and veg they like.
This may sound "woo-woo" but get them involved in the land and the wheel of the year. Just for example, pomegranates are in season right now, plus persimmons, cranberries, apples, pears, brussels sprouts, winter squash, sweet potatos, etc. Could possibly do a "family" activity like berry picking, apple picking, foraging for mushrooms, etc. at the right time of year.
Longer term, would they be interested in growing anything - even in pots if you don't have a garden or access to an allotment?