Over a 7 - 10 day period, mix the diet with your pet's former food, gradually increasing the proportions until only the new diet is being fed. (mscc.ca)
It is important to pick a loose seed mix diet that contains a variety of foods such as grains and dried vegetables along with some seeds. (thesprucepets.com)
It is unlikely that there would be any problem with using soy as part of a good mixed diet in an older child. (cyh.com)