My four year old granddaughter helps me plant seeds, mulch, even weed. Trick is to make it fun and educational. Like when mulching we always say, "Snug as a bug in a rug" so she knows he is doing something to help/protect the plant. When she plants seeds we just check EVERY DAY to see if anything is "popping up,"and I use my finger curled up then gradually uncurling to represent the seed sprouting and pushing through the soil. Maybe let some seeds sprout in paper towel? I show her how to weed correctly, even knocking the soil off the roots, and how to identify the seedlings or perennials peeking through, like peonies. She can identify buds and knows they will be flowers and she knows when the flower has died it produces seeds. But every child is different and you'd just have to play it by ear to see how interested she really is and how much she grasps.
Now my granddaughter has been coming to the garden with me since before she could walk and she already knows lots names of flowers and can identify peas, beans, corn, garlic, etc. But if your neighbor's daughter is really interested, give her mini lessons unless she wants to hang around, and just keep repeating things. When my granddaughter was two she helped me dig a 50' row of potatoes and she stuck it out for the whole row. She loved standing on the fork to push it in (I did one side, she did the other), then pull, pull to leverage the fork and lift the potatoes out. What a magical surprise to find the potatoes! Of course, I still feel that way myself!
