fact time:
the total eclipse will not be visible from the UK. We will be able to see a good partial eclipse, up to 90% coverage in the north. Even the south will see good coverage.
the Sept 28th total eclipse is OF THE MOON.
it may be cloudy of course. But even if it is intermittently cloudy, it will still be quite a spectacle as light levels drop, animals react and shadows show the part-covered sun.
do not even think of using sunglasses, smoked glass, camera film or any other daft ideas. Proper eclipse glasses will not let you see anything else so you can't walk about in them. Driving is serious Darwin award stuff.
supervising children will be challenging - they must keep their proper eclipse glasses on throughout the eclipse (over 2 hours) while they are outside, unless you can trust them not to look at the sun. The reduced brightness will stop the normal inability to look at the sun, but there is still plenty to cause eye damage.
If the school isn't doing anything, I'd send them in late if you can get the time and supervise yours with pinholes/colanders etc. This is science and nothing is more important.
animation; set for your location
www.timeanddate.com/eclipse/solar/2015-march-20