My 4 year olds loved their first live circus show. Stared, open mouthed for the whole 2 hours. We got there really early and enjoyed the atmosphere before the show.
I have learnt from past experience, however, that if you go to the circus in February take extra blankets. Even though there are heaters as it was only 2 degrees C outside, stormy and windy, of course it was cold inside too.
John Lawson is one of the cheaper circuses, making it more affordable for families but still good value for £££: entertaining, great costumes and skills that most of us mere mortals do not have. I think not so much the result of talent as of years of hard work.