boarding pass beat me to it - in no way do any of us have the right of leeway with SOP's the clue is in the name - if your company has a standard operating procedure you are legally bound by your contract of employment to comply with it, anything else - regardless of safety risks - certainly puts your job at risk and puts those who stick to SOP's in a difficult position.
If when flying I did something that was "legal" but nevertheless against a company SOP they would have my balls.
That said SOP's are not always that clear cut - those who have had recent recurrent training at BA will know that calling the flight deck on t/o roll is normally prohibited however they are training scenarios where fire is suspected to have broken out on the runway - and in this case they are saying yes it is okay to attempt to make contact with the flight deck. It is deemed to be within the scope of the SOP.
Similarly if you are on final with the only option left to you the physical restraint with handcuffs of a 2 1/2 year old and their parent or a lap belt what are you going to do (well as main crew you are going to ask the Purser and/or the Flight Crew).
I would suggest though that in a situation like this it should be pointed out to the parent that in no way is the situation acceptable. It is not okay just to say oh well it's against an SOP but it's not illegal therefore I will hand over an extension seat belt without further explanation or investigation.
So in conclusion SOP's are their to be followed and not lightly pushed aside on a whim - only when it becomes dangerous not to use common sense is it okay.