my mum was wondering about blue tits

[spillergent]

hello my mum was wondering about blue tits that use her nest box they get half way through rasing there young but every year desert the young and my mum does not notice until it to late i have protected the box from cat attacks and we leave them to it by not going near the box when in use any one got any ideas what might be happaning

[SheffieldLass]

Hi
It sounds as if something is happening to one or both of the parents ... possibly killed by cats, as it sounds as if you have cats around. They don't usually desert the box when the young have hatched.