Type something like..... On (//) (whatever your son's name is) was given a DLA award which I have notified you of and already in receipt of the extra disability element so that's great, however now on (//) (whatever your daughter's name is) has been also given a DLA award. Please can this be backdated to (//) as this was something we have been awaiting a decision on. Thank you.
Then if you have another carers to put on make sure you change the caring status too