Yes, this should work well.  It is entirely possible.  I'm assuming that these will be of a display type size.
For vehicles etc.  my suggestion (and there may well be other, more intelligent ones) would be to use cardboard to create the basic structure.  You can introduce a really good design element, if they are of an age to think in three dimensions . . . .
1  freehand drawings of what they want it to look like;
2  rough plans for top /bottom /sides/ front /back to see if they are thinking 'constructively';
3  careful drawings in actual size of all the component parts;
4  transfer drawings to card (cereal packet may be adequate) and cut out;
5  join the sections together - hot glue is best and/or masking tape;  slow setting glue is not helpful at this stage;
6  use paper laminating technique to cover and strengthen and add further features.
7  paint.

How does that sound?
DavidO

8) Nice one, Sue.
The cardboard boxes used for the Kelloggs cereals mini packs ought to be useful.
You can get two stroke engines from old lawnmowers too!!!
DavidO

4 hours?    Nope   :cry:

The main thing about paper work is that you must include drying times.  Would you have a warm area (conservatory type) for stuff to dry over lunchtime?  Or intersperse other activities.  Or split across two days.

Try it out with a sample child as soon as possible and then plan your times.
DavidO