As one might expect this topic has proved to be a little underwhelming. I have found no information from N. America or Europe, but for the U.K. the position has been clarified by the FBHVC and, with permission, I reproduce their advice here:
'Seat Belts
Requirement for seat belts to be fitted
Cars and light vans constructed after the end of 1964 but prior to 31 March 1987 must be fitted with seat belts for the driver’s seat and outer passenger seat (if fitted.) No belt is required for a central front passenger seat.
Cars and light vans constructed after 1 April 1987 must be fitted with belts for each seat. Central seats may be lap belts only, others must be lap and diagonal.
Requirement for seat belts to be used
The law requires drivers and passengers in cars and other light vehicles to wear seat belts “if available”. There are stricter requirements for children (see below.) The general position in Scotland, England and Wales is contained in Statutory Instrument 1993/176 The Motor Vehicles (Wearing of Seat Belts) Regulations 1993, as subsequently amended by S.I. 2006/1982 The Motor Vehicles (Wearing of Seat Belts) (Amendment) Regulations 2006. Similar rules apply in N. Ireland.
Ignoring the special provisions for the disabled, those with medical certificates, those using delivery vehicles or travelling in taxis, the regulations can be summarised as: if the seat has a belt, anyone using the seat must also use that belt. This applies whether or not the motor vehicle concerned is required by Construction and Use regulations to have belts fitted – in other words, if you have belts in your pre-1965 car, you must use them even though there is no requirement to have them there in the first place.
Requirements for children
Children under three years must use a child restraint (ie child seat or booster) appropriate for their weight in any vehicle (including vans and other goods vehicles) – so they may not be carried in any vehicle unless it is fitted with the appropriate restraint.
In vehicles where seat belts are fitted, children three years and over up to 135 cm in height (approx 4ft 5ins) must use an appropriate child restraint for their size rather than the adult belt. If no belts are fitted, they must travel in the rear seat. If there is no rear seat, they may not travel.'
You can find the full version on
http://fbhvc.co.uk/seat-belts/ however the concern I raised is covered in the last two sentences of the above paragraph. In short, in an old two seater car, first used prior to 1965 and not fitted with seat belts, you are forbidden to give a ride to any child below the age of 14.
Please do not forget that this applies in areas other than the highway as the Road Traffic Acts now extend to cover other areas, here is a brief extract to give you an idea how widely Traffic Law can be applied:
'Most of the provisions apply on all roads throughout Great Britain, although there are some exceptions. The definition of a road in England and Wales is ‘any highway and any other road to which the public has access and includes bridges over which a road passes’ (RTA 1988 sect 192(1)). In Scotland, there is a similar definition which is extended to include any way over which the public have a right of passage (R(S)A 1984 sect 151(1)).
It is important to note that references to ‘road’ therefore generally include footpaths, bridleways and cycle tracks, and many roadways and driveways on private land (including many car parks.) In most cases, the law will apply to them and there may be additional rules for particular paths or ways. Some serious driving offences, including drink-driving offences, also apply to all public places, for example public car parks.'
You can now see the full problem: If you give a ride to a youngster at, say the A.C.O.C. National Day, and the field you are in has a footpath across it you may be committing a criminal offence.
I hope this madness is restricted to the U.K., but as it results from a Brussels directive withdrawing the U.K. Exemption,as previously noted, I expect that all E.U. States will be in a similar position.
I suspect that it would be impracticable for a driver at a Club event to determine the legal status of the venue with regard to the Road Traffic Acts so that the only safe course is to deny any child, under 14, access to old vehicles.