To make gardening fun/interesting for kids, here are some things you can do to get them to have some interest in it:
Grow Stuff that is FUN! Last year we grew yellow grape tomatoes. The kids LOVED the fact we grew yellow tomatoes. I'd even let them play with them - because, well, why not? There are so many fun and interesting things you can grow these days. Experiment!
Give them a job. Make it your child's job to pick the produce. Sure - they might pick some stuff that isn't quite ripe or drop some or squish some. Whatever. Let them be involved. They'll be more into it.
Grow a Green Bean Teepee! What better way is there to get your kids into gardening? Make them a teepee in it! You can grow green beans or cucumbers or any vine vegetable on them.
Make cheap signs. We used some spare wood in the basement and made some signs. The kids loved it. It doesn't have to be fancy or Pinterest worthy. We used a black Sharpie marker.
Start some plants from seed. Kids love planting stuff. They are impatient - but it's fun to watch the little sprouts start to emerge. This also teaches kids how the plants start and whatnot.
Remember - the last frost in Massachusetts is around mid-May. So you don't want to hop on the bandwagon and throw stuff in the ground quite yet. But it's good to plan and think about what you might want to plant this year. I'm so excited for spring!