These conifers do go brown at the bottom as they get older. The ones that are going brown higher up may be suffering from wind burn or drought or they may be diseased. But there is absolutely no danger whatever to your children.
Sadly it is very unlikely that the brown parts will recover though if its wind damage they just might.

Not sure where you are Timeboy, they are very densely packed and as Stera says drought, wind, heat.....its been an odd summer this year
sadly she's right too about the dead patches......I've never known them to regrow.....

So will I be ok to cut the dead bits off? Thanks for your help

I would cut everything off, in fact remove them completely - they will look dreadful for ever if left.

Agreed Landgirl....the soil will be in need of some TLC, the trees will have leeched all the moisture and nutrients from it