Early Impromptu Improv. That’s what you can do spur-of-the-moment when something like this happens: your pre-note-reading siblings arrive with worried smiles and one says, “I forgot my instrument.”
“No problem,” you say, “I have several others around the studio.”
“And my books…”
“…and I forgot what you showed me last week.”
The younger sibling chimes in (with frank cheerfulness), “I don’t have any of my piano books either!”
Instead of various reactions of a negative nature that spring to mind, you could do an Early Impromptu Improv with them.