You must fill out a separate questionnaire for each child, attach photos. Children are now included in the parent's visa, so a child's visa is provided free of charge. Consular fees will be charged in full for the issuing and processing of visas for children and adults.
If you cannot obtain the consent of the other parent, you must provide a certificate stating that you are a single mother or that the child's father is unknown. Your message, even a notarized one, is not going to be enough. Don't forget to attach children's birth certificates to the applications, copies must be made in advance.