Kids are busy. With extra-curriculars, homework, school; but also with their free play and imagination.
A kid hardly ever just walks up the stairs. They scale Mount Everest.
A kid hardly ever just eats a sandwich. They wonder what a peanut butter factory looks like.
A kid hardly ever just brushes their hair in the mirror. They ponder what they can do to avoid a hurtful comment from that one kid at school.
Whether imagination or anxiety, many kids are stuck in their heads for much of the day.
Then, it’s time to practice. Playing an instrument requires their whole focus. Their Everest expedition is on a break and now they’re focusing on their balance, the angle of their fingertip, the quality of the sound. Playing an instrument requires a lot of focus on their body. All of a sudden, they’re focusing on their physical sensations for maybe the first time all day.

As their mind processes whether they need to move their fingertip a millimeter to change the intonation, all of a sudden they start to sense, “huh, my throat’s a little scratchy, am I thirsty?” They focus on the balance of their violin while they do a big shift and they notice, “wooah, my bladder is way more full than I thought.”
Practicing music can be meditative–that’s one of things I love most about it. Meditation invites awareness of sensations that we put off all day. Sometimes that’s emotions we’ve pushed out of the way. Sometimes that’s nagging tasks we haven’t had time to think about. Sometimes that’s physical sensations inside our body.
Some kids can struggle with interoception– the sense of what’s up with their own body. For kids who live very much in their brains (I was definitely one,) they have a tough time understanding their body’s cues for everything from hunger to emotional regulation.
Music can be a time to get embodied. They can focus on their sensations and how their body feels.
Do some kids use water/snack/bathroom requests as a delay tactic? Sure, that definitely happens. They may need to a) gain comfort with the discomfort of working on something difficult, and b) build trust in their parent or teacher to stay calm when things are tricky. The delay tactics begin to fade over time.
These delays can be really irritating and take a third or more of the practice time available. But, in my opinion, they are a feature not a bug of the meditativeness of practicing music. Next time your child is driving you crazy by asking for water all of a sudden you can think, “They’re getting embodied right now. Mission accomplished.”