Both kids love playing with water so they each have little plastic watering cans, which have been fun additions to our Water Table play and kiddie pool.
They also love to imitate what Bill and I do. We planted tomato plants in pots on our back deck this year and both kids eagerly want to participate in watering all our plants. So yes, we let them "help". They enjoy it so much that they ask to water the plants.
Letting Matthew use the big watering has added benefits for him. A half-full big watering can is heavy enough to improve his muscle tone. He learns to gauge how much "power" he will need to apply to lift the watering can. He learns how to hold it upright to minimize spills as he walks from the faucet to the plants. He learns to hold it different way to water the plants.
It is considered a "heavy work activity". Many books on sensory processing talk about heavy work activities as a way to provide proprioceptive input to the body. According to a site called Sensory Processing Disorder,
Proprioceptive input is the performance of tasks that involves heavy resistance and input to the muscles and joints, and is essential in helping our bodies assimilate and process both movement (vestibular) and touch (tactile) information.
Intense proprioceptive input has been beneficial for Matthew. He doesn't have an "excessive need to crash and bump into objects, walls, and people" like the Sensory Processing Disorder website describes wherein the input is calming. On the contrary, I believe the right intensity of input helps awaken and stimulate his muscles and nervous system thereby helping him attend better to an activity and allowing him to get more out of the experience cognitively.
Since Elizabeth can't manage the big watering can yet, she's content using the little plastic one.
She's also more than willing to tell Matthew where to water. "There!" she says, as she points. She's proving to be quite a natural at directing.