Thank you for your question
My name is ***** ***** I am so sorry for your loss
How old are the children
They are your son's "next of Kin" - a phrase which refers to his nearest relatives
If your son left a Will then it is for his Executors to deal with his Estate - if he did not then his former partner has the right to do it on behalf of the children.
Please ask if you need further details
What assets did he have?
What is it that you want to know about the position
She cannot do so - you paid for it and you get to chose the wording