Paid for flight was refused due to birth certificates

I booked and paid a flight with Safair from George airport to OR Tambo. I have been flying with another airline with my children for the past 7 years and always use my ID and their medical aid cards for identification. Today when i tried to book in safair refused to book me in if i dont show the children's birth certificates. I had to drive home to get it and missed the flight. Safair then said that i can get onto another flight tomorrow afternoon but that it will cost me R900 extra. The rest of the airlines except the medical aid cards. It is however the total abrupt attitude from Safair that i found extremely unpleasant. They should then warn parents about this new rule in bold on the website. I had to book with another airline to be in time for my appointment and that cost me an extra R2900.