The goal of this observational study is to compare the incidence of ARI and/or diarrheal disease associated with feeding different formulas with and without lactoferrin supplement in children of 2-3 years old. 200 children eligible for the study will be enrolled from two study sites and randomly assigned to two groups (a2 growing up stage 3 formula puls lactoferrin supplement, and Enfinitas growing up stage 3 formula) to feed for 90 days. About 160 children (80 for each group) are expected to finish the study, and data will be collected during the four visits across the study.

Researchers will compare the two groups to see if there is significant decrease of the occurrence of diarrheal disease and/or acute respiratory infection for children fed with a2 growing up stage 3 formula puls lactoferrin supplement

This study is two arms, opening parallel-designed, observational study. Diarrheal and infectious episodes, including acute upper and lower respiratory infections (ARI), changes in stool patterns, use of systemic antibiotics, adverse events and study formula consumption will be compared in children 2 - 3 years of age who are assigned to receive one of the two following study formulas for a 3-month feeding period: a2 growing up stage 3 formula puls lactoferrin supplement and Enfinitas growingup stage 3 formula.

200 children eligible for the study will be enrolled from two study sites and randomly assigned to two groups to feed for 90 days. About 160 children (80 for each group) are expected to finish the study, and data of primary and secondary outcomes will be collected during the four visits across the study. A sample size of 80 completed per group is needed to achieve a 80% power.

The Andersen-Gill model will be used to model the primary outcome (recurrent event of either diarrheal disease or an acute respiratory infection) under the framework of the proportional hazard assumption. For other secondary outcomes such as duration of acute respiratory infections(ARI) and/or diarrheal disease, episodes of systemic antibiotic use,amount of study formula consumed,changes in stool pattern and cost of treatment will also be analyzed.

Inclusion Criteria:

• Full term born children current aged 2-3 years old
• Birth weight not less than 2500g (5lb 8oz)
• Consumes Milk or milk-based beverage regularly before recruitment
• Informed consent signed
• Parents or guardians of the infants committ not to participate in interventional clinical research during the intervention

Exclusion Criteria:

• Has a potential risk of metabolic or chronic disease; Fetal malformation; Or present with condition(s) that the investigator believes may affect the infant's ability to be orally fed, the infant's normal growth/development, or the infant's health evaluation.
• In-take prebiotics or probiotic continuesly 15 days before the recruitment.
• Growth problems or other protencial risks.
• Larger-gestational age (LGA) babies born to mothers with gestational diabetes (defined as newborns whose birth weight is above the 90th percentile of average - Treated with antibiotics 7 days before study intervention.

Full term born children who are 2-3 years old and consume Milk or milk-based beverage regularly