Am I sinful or blameworthy for refraining from communicating with my children who live with their father, after I asked them to go to him, and they are shunning me and not asking about me?

The default is the obligation to maintain ties with children and the prohibition of cutting them off for more than three days, unless the cutting off is for the purpose of disciplining and reforming them. In that case, it is permissible to cut them off, even if it exceeds three days. The issue of shunning disobedient children is subject to the benefit hoped for from the shunning. It is generally the case that maintaining ties and showing kindness, along with continuously enjoining good and forbidding evil and striving for reform, is more beneficial and preferable than shunning. Therefore, strive to reform them, do not despair, seek the intervention of righteous people, seek help from Allah Almighty, and supplicate for them frequently, for the supplication of a parent for their child is answered.