Can I take my daughter's anywhere?

Hi, I'm a mother of two 16th and 10 y/o, my kids have no father on their birth certificates and both birth certificates are late registered. I've tried to apply for a visa to get out of the country with both my girls but they've been denied due to I can't provide an ultrasound and hospital records of birth. Is there a way for me to get any documentation that will certify me as the sole legal parent of my kids? Thank you in advance for your kindness and response it's really appreciated.