Hi, thank you for your question. Just a bit more information required to fully assist you:
-Are you in England or Wales?
-How old are the children?
-How long have you been with the father and is it a long-term relationship?
-What were the previous arrangements for the children?
-What arrangements are sought now?
Thank you. Firstly, you have no rights to contact with the children. However, given you are in what appears to be a long-term relationship with the father it would be expected that you would have contact with the children and they would likely be aware of your relationship. The mother can only reasonably restrict the father's contact arrangements if there are welfare or child protection concerns and this can include emotional abuse/distress. However, she cannot prevent all arrangements just because she does not want you involved. If she does this the father should apply to the children's local family court for a child arrangement order using form C100 and a £215 court fee.
I hope this assists you. If you found this information helpful please provide a positive rating using the stars at the top of this page. I will not be credited for your question without a positive rating. Thank you