Is it safe to use children's Benadryl (diphenhydramine) with hylands cold n cough for kids? My daughter is 2.

No. Cough & cold medications are not recommended for children under 4 years. They do not make colds better, shorten how long a child is sick, or prevent a child from worsening, & they can be dangerous. Coughing during the day helps your child keep her airway clear. If she cannot sleep at night, try a cool mist humidifier, a teaspoon of honey or saltwater nose drops. Good info here: kidshealth.org.
The American Academy. Of pediatrics recommends that over-the-counter cough & cold medicines not be given to infants and small children because they have not been proven effective and can be harmful. Discuss other ways to treat cold symptoms with your doctor, & have her checked if the cough lasts >3 days.Benadryl (diphenhydramine) is for allergies. Hyland's products aren't fda-approved; the syrup contains ipecac & phosphorus.