When best to inform of a change (disabled son no longer a QYP)

Hi again

I have a client scenario and I just want to check what the best course of action for her is.

Client is married and has a 19 year old severely disabled son.  Her husband works part time and she gets CA.  They receive UC including the child element and disabled child element.  Her assessment period for UC starts on 15th of the month.  Her son attends a specialist school and will be attending college from September (non-advanced).

Client’s son turns 20 on 25th November. At this point he is entitled to claim UC in his own right and the client’s child benefit will stop.  Now, for the child element and disabled child element will this automatically stop when her son turns 20 OR only when she informs UC?  As this “change” occurs during the assessment period, can she wait until 16th December to inform UC and for her son to claim UC?  If she informs them on his birthday, won’t this change “remove” the child element and child disabled element from 15th November, the start of the assessment period?

For when the son claims UC - as he’s on PIP he should be treated as having a LCW for UC?

Many thanks as always.

* CB is payable to 20th birthday but UC regs state up to 1st Sept following 19th birthday so this would give a gap between 01/09/18 and when he turned 20.  As CB would still be in payment, would UC still pay both child elements or would these stop on 01/09/18?!  Would they be better off as a family with the son claiming UC from 01/09/18 as from what I’ve read the child elements will stop on 01/09/18 even though CB would continue?