The best option for baby squirrels from 4 weeks of age through weaning. Fox Valley Formula 20/50 is also ideal for flying squirrels, rats, and mice. This rehabber-approved powdered milk formula produces better weight gain, fewer digestive problems, and better acceptance than other formulas. Fox Valley Formula 20/50 mixes easily, smells wonderful, and there is no need to supplement the formula with any added cream, yogurt, or probiotics.