Actually, it wasn't a very good kite.
5 seconds sound clip from the Mary Poppins movie soundboard.
You can hear this line at 00:15:56 in the Blu-ray version of the movie.
Quote context
[...]
- Well?
- I'm sorry we lost Katie Nanna, Father.
- And the kite was too strong for us.
- In a manner of speaking, sir, it was the kite that ran away, not the children.
- Thank you, Constable. I think I can manage this.
- Actually, it wasn't a very good kite.
- We made it ourselves. Perhaps if you helped us to make one...
- Why, only last week with me own youngsters...
- I'm very grateful to you, Constable, for returning the children.
[...]