Before you ask permission, you should have a plan. Your plan need not be much more than a secure, stable hold and a basic flight path.
Before you make a plan, ascertain the child's fitness for flight. Does the child seem sturdy and resilient? Does the child seem easily spooked? Does the child seem to trust you?
When you ask permission, take several steps. Would you like to be an airplane? is a good first question. May I pick you up? is a good second question.
If the child says yes and yes, give him advance notice before flight. A basic countdown will work.
No airplane can fly without wings and an engine sound. You need not provide these things; you will provide the lift and maneuvering. Ask the child to practice his engine sound. Remind him to keep his wings outstretched.
After take-off, monitor your small new airplane with great care. At the first sign of trouble, bring him in for a soft landing. If there are no signs of trouble on the test run, come in for a landing and check over all flight equipment. When he tells you he's ready to fly again, start a countdown if you feel able.
When the time comes for a rest, tell him the engine needs to recharge for three minutes. Make three minutes last seven.
When you and your airplane have gotten more comfortable with one another, experiment with fancy flight patterns. Small dips and soars will thrill your airplane. Do not attempt a barrel roll with a plane you've made from someone else's child. A tailspin will thrill your plane. Avoid crash landings. Protect your plane's propeller at all times. Do not force him to keep his wings spread if you fly him in modified loop-de-loops. (Always modify your loop-de-loops.) Explore your territory. Find new territory. Visit the fireplace in the corner of the yard. Search for more dandelion seeds to blow around. Avoid the broken glass you found on your first reconaissance mission.
Return to home base between flights. Make a thirty-second countdown last three minutes.
When your airplane's mother wonders how you've managed to transform her child, offer to teach her how to do it herself. Encourage her when she traps one of his wings on the wrong side of her arm. Remind her that no airplane can fly without wings and an engine sound. (Do not tell her the story about the time you swung a child around by his ankles and he, laughing hysterically, wriggled and then fell out of your hands. Your hold was neither stable nor secure that time. You know better, half a lifetime later.)
When your airplane returns to you later, ask him if he'd like to be a train. Take turns being the caboose.
Do not let him try to turn the dog into a horse. The dog cannot give permission. The dog will not neigh.
When your airplane must take his leave of you, hug him goodbye. When he (exhausted) protests against leaving his pilot, welcome him to the human condition.
Know that you will probably never see your airplane again. Know that he will remember you, if at all, as only an arm across the chest and an arm across the legs. A tight hold. A swift dip and fast turn. A lifting off of the ground and a rushing of air. A pair of black-shod feet pounding over green grass. A reminding voice in the ear: Don't forget your wings. Don't forget your engine.
(That's last Wednesday's tree: what a weekend of warmth will do. And I passed my review. Now, onward to tenure.)