squeezing in stonehenge from bath to london

Renting a car is likely to be the easiest for most in this situation.

Alternatively, you can join a bus tour leaving from Bath and either do it as a day trip while you are in Bath or just take it to Stonehenge and forfeit the return journey. I'd imagine the bus would be happy to look after your luggage while you look around.

The other option is to take a coach/bus or train to Salisbury and then take the Stonehenge special bus to the site. I don't think there is left luggage facilities there. I am not sure what they do at Stonehenge but I can't imagine you would be the first tourist with luggage. Afterwards you can make your way to London.

I guess the other thing this would depend on is the age of your children and their ability to cope with such a long travel day especially when lugging bags on public transport. Don't underestimate what a hassle that will be even to the lightest of travelers.

Jenufa's advice is about as good as it gets. I can say that most of the tour companies have guides, and the drivers stay with the buses while people visit (so you luggage should be secure). You could try this web page:http://www.discount-london-tours.com/stonehenge-tours.html
details of Stonehenge and local bus service:http://www.visitwiltshire.co.uk/salisbury/about-the-area/5-000-years-of-history/stonehenge-britains-best-historic-site