Advice on catering for mixed-age family events?

Family’s planning a multi-generational get-together next month—grandparents down to toddlers—and they’ve asked me to sort the food. Honestly, I’m a bit lost. We need something that’s easy to serve, appeals to different age groups, and isn’t just fast food. A buffet came up in conversation, which sounds promising, but I’ve never organized catering before. If anyone here has done this kind of thing, especially in Sydney, I’d love some pointers or suggestions. What worked for you? What should I look out for?