My thinking about this is that state run schools should take into account that the children attending them are not all from Christian homes. There will be Muslim, Jewish, atheist, agnostic humanist, perhaps Buddhist and Hindu homes represented amongst the children, as well as any denomination of Christianity you can think of.
This being so, morning assemblies should either be abolished, purely secular - a means of strengthening the school as a community by begining the day together, or if they are to have any form of prayers, these should be strictly rotated amongst the faiths the pupils and staff belong to.
Parents who wish their children to receive instruction in their own religion should either send their children to a private school, lobby their MPs to provide state run schools that are divided along doctinal lines, (not that I think this would be a particularly good idea, as it would undoubtedly lead to narrow-minded sectarianism) or schedule religious instruction for their children as after-school activities.
If you, as I, feel it sad that so many children grow up without any idea of what the religion they nominally belong to has to offer, then we - by which I mean all adult believers, should be doing what we can to encourage whichever religion we belong to, to do more to attract the curious.
In other words, get off our backsides and run Sunday schools, Thursday evening classes in the synagogue, groups in the mosque etc. Or go out into the streets, as various groups did formerly and engage the interested in a discussion.
When did you last see the Salvation Army singing hymns in the local square, or a Franciscan or Dominican friar preaching at a street corner? Or even a nun, monk, priest, parson or Lutheren deaconess in a habit in public? Or a Jew wearing his kippah?
When we relegate religion strictly to the private sphere, we can hardly wonder it declines.