Knocking him out might have been a good option. A fun one, too-- a crack on the head would be cathartic and save Iron Man from having to worry about what further trouble Pietro was inevitably going to get into. Hard to account for Pietro's recovery rate, though. Harder to get that one by Fury. Quicksilver, speed demon, 'fell down the stairs' is a hard sell.
"You don't have to know that," Iron Man replied, but he held Quicksilver just by the back of the shirt then, turning away and pinpointing where Wanda was located. Keeping Quicksilver reminded that he was not part of this operation was important, but Iron Man also wasn't keen on giving him an 'I have no idea' answer. Luckily, as much as Pietro's last question would elude him, the receiver in Wanda's ring was telling him they weren't on the move anymore. Iron Man looked back at Pietro, Tony's face scrunched in annoyance, but had nothing to say to the interfering sibling over the gentle lap of waves behind them. He just pointed a threatening finger at the young man, then snapped him back against his side to take to the air again.