Child comes onto ward and:
sticks hand inside sharps bin
trips patient during therapy session
Jumps over beds/climbs over furniture
Adjusts pump/equipment settings
Sticks finger in patient wound
All examples I've witnessed first hand, two of which were on acute stroke units. Without wanting to sound rude, your understanding of a stroke unit is the experience of visiting a patient, so very limited.
You're right that a visiting child can be a real bonus for patients, but they can also be a proper pain (as can a lot of visiting adults actually).