Gardening projects need to be tailored to children of different ages.
www.kidsgardening.org has some great suggestions about what kids are interested in at different ages. Here are some ideas:
The little ones
Ages 0-3. Babies may not be able to garden on their own but spending time outside can be vital to their development. As their brains mature the stimulation of outdoor environments helps develop their senses. Let them smell, touch, hear and even taste the world around them. Being close to parents in the garden also offers time for bonding.
In the beginning
Ages 3-4. Gardening is great fun. Toddlers love to move mulch, catch insects and pull out a few weeds. This age is about exploration and experimentation, with adults on hand to help. Kindergarten garden: Age 5. This is the time to start creating forts, tree houses, secret hide outs and developing a special space in the yard just for kids. Let the children take the lead and assist only when needed. Let them get messy and create their own projects.
In the middle
Ages 6-7. Now that kids have some reading and math skills this can add to the fun. Now is the time to get them reading seed packets, selecting the right plants for a certain environment and paying for them at the local nursery. Soil, holes and water are all exciting.
Ages 8-9. Now that children are becoming more independent they can start having more input into the type of garden they would like. They can plan out the garden on paper, select and purchase plants. Learn to think about species, flowers, plant height and fences. They are also ready to start using gardening tools. This is the time to appreciate not just the process of gardening but the end reward. It's a time to plant flowers and vegetables that offer an end result.
Ages 10-12. Now it's time to get involved on a bigger scale. Kids of this age can take part in community gardening projects and tree planting groups. They can also let their imaginations run wild on a range of projects. Whether that be selling seeds, making their own worm farm from scratch or building a scare crow that looks like their favourite book character.