it is actually illegal to cycle on the pavement.
Rule 64
You
MUST NOT cycle on a pavement.
Laws HA 1835 sect 72 & R(S)A sect 129
However, children under the age of 10 in England, Wales and Northern Ireland and under 12 in Scotland are below the age of criminal responsibility. Therefore, they cannot be prosecuted for a criminal offence. They cannot be issued with a fixed penalty notice either as they cannot be given to anyone under the age of 16.
This means that, whilst police officers can theoretically stop young children (aged under 10 or 12) who are cycling on pavements, they have no powers to arrest, fine or even caution them. This is sensible, as young children should not be expected to cycle on the road. To prepare them for this step as they get older.
In any case, there are no powers for the police to confiscate pedal cycles being ridden on the pavement, not for cyclists of any age.