They will plant crooked rows, dump a handful of tiny seeds in one spot, and dig up the bed you've just planted.
They'll pull up the spinach and leave the weeds, trample the strawberries, knock over the bean trellis, pull the carrots before they're ready, and eat all of the raspberries before you get even one.
They will talk your ear off. They will ask "Why? Why? Why?"
They will say, "Look! Look! A ripe tomato! Look, here's a cucumber! Wow! A butterfly! Look at the sunflowers! Look, what I found!" And they will insist that you actually stop and look and marvel right along with them.
They will grow up to be gardeners.