Kylie, I'm feeding our babies twice a day & depending on the condition of the water...it is either partially or fully changed. I have plenty of prepared water stored for them.
All fish get stressed when their water is being changed, it's inevitable, however, axolotl larvae are somewhat resilient & our babies are healthy.
You might want to read the following;
Rearing Axolotls
http://www.axolotl.org/rearing.htm
Very young larvae can be kept together without much risk of cannibalism since this really only begins once the front legs develop. When very young they should be fed frequently (once or twice daily). If kept at about 20 °C (68 °F) they should reach about 1.5 cm in length within a week. The larva pictured on the right is four days old and 14 mm in length. It is D/D M/m a/a (see the Genetics Page for more information about colour). If feeding brineshrimp, at least some of the water should be replaced each day because newly hatched brineshrimp die quickly in fresh water and can foul the water in a matter of hours. As mentioned above, Daphnia will live in the tank with the larvae until eaten, so occasional water changes are fine (partial water changes a few times a week).