The problem with the flying number was that Williams was unable to stop herself from turning around on the wire. The other problem was the camera angles shot from the side of the set instead of straight on, this made the wires very easy to see. Usually the wallpaper on the Darling Nursery set has stripes. Take a look at the Duncan video --the wallpaper on the set is going up and down so the wires will blend in.
When they flew out the window the whole thing just came to a dead stop. It looked like they were trying to do things they had rehearsed but were unable to. They were not able to look like they were flying, they looked like they were just hanging.
Williams is truly awful as Peter. No charisma, wooden line readings. Honestly, I've seen children in community theater productions bring more excitement to the
role. ANd I can prove it. This is not video from the actual production, they are just doing a number (Ugg a Wugg) for a THeater Awards ceremony where this production (including its 13 year old lead) was nominated.
https://www.youtube.com/watch?v=lR4VagoKVb0