I say we could maybe start with them around 2-5 years old, and every once in a while we could progress and skip some time to make them older (like if a major chapter is closed) idk though it's just an idea-
Also, remember Nublada had that small cloud and granted Dust the wish earlier (when he gave her the ring)? Each member of the Dream Kingdom's royal family lineage inherits this ability, meaning both children would have the ability to grant a wish for someone in their lifetime because Nublada is connected genetically to King Stratus. Also, they can visit the dream world for brief periods of time, since they don't have Nublada's crown. And if Dust has any genetic abilities (ones that come from his ancestors) they could be passed on as well.