Kids are indecisive creatures who randomly change their mind at any moment, and as such you should always wait.
Let me explain.
Let’s say you make toast, butter it, spread something delightful in it, and get ready for them to take it.
It’s likely they’ll need that thing cut, more butter, more jam more of something else, who knows.
So just wait, hold the knife in bated breath, don’t move, just hang, it’ll come I promise.