livebearers in general, guppies included, are usually hardy and quite forgiving of water issues. However there is an issue with loss of vigor in livebearers that have been line bred to intensely without sufficient outcrossing. So you may be fine with your normal husbandry practices or you may need to do additional work for them.
Young fish in general are more sensitive than adults, and that includes sudden changes in water parameters that could be caused by large infrequent water changes. It would be better for them to do smaller water changes more often with young fish in the tank.