It's my understanding that the 'police check' mentioned (formally called 'enhanced disclosure') would only be necessary if you were to be left in sole charge of children.

In all cases in primary schools (which is the age group you are thinking of, Allison) in my experience as a primary school teacher, teaching staff would also be present with a visiting speaker or entertainer, so this formality would not be necessary.

The problem of school holidays is significant, although many primary schools might include such an event as an end-of-term 'treat'.

Another idea would be to get booked at say Whitby and Sidmouth festivals, which are each a week long and both run childrens' workshops. I think they'd love you, but the problem could be that your name isn't known- if you have influential friends/contacts on the music scene that would help a great deal. Same applies to other, weekend festivals, but possibly to a lesser degree.

Hope something works out for you.