To evaluate the intervention effects of Bifidobacterium animalis subsp. lactis strain BLa80 in promoting growth and development (including gut microbiota and physical growth and development) of healthy infants and young children across different age groups, enhancing immune function, improving allergy incidence, and analyzing the safety of BLa80 in relation to infant growth and development, allergy incidence, and gut microbiota.

Inclusion Criteria:

1. Healthy infants and young children born at 37 to 42 weeks of gestation through both artificial breastfeeding, with a birth weight greater than or equal to 2500 g and less than 4000 g, regardless of gender
2. Infants and young children whose mothers do not have diagnosed metabolic disorders such as diabetes and are not afflicted with communicable diseases such as hepatitis B or HIV
3. Enrollment will be stratified into three age groups: 0-6 months, 6-12 months, and 12-36 months
4. Consent from parents or primary caregivers of infants and young children to collect faecal samples during the study
5. No clinically diagnosed allergic diseases at the time of enrolment (including but not limited to eczema, asthma, allergic colitis, allergic rhinitis, pollen allergies, etc.)
6. Infants and young children with a medical record established at local maternal and child health care hospital's paediatrics department, undergoing regular check-ups, and following feeding advice and guidance from pediatricians
7. Assurance from family members or primary caregivers not to administer additional probiotic products (including formula milk containing probiotics) to infants and young children during the intervention period.

Exclusion Criteria:

• Healthy infants and young children aged 0-6 months:

  1. Infants with a history of asphyxia at birth or a history of NICU hospitalization
  2. Infants born with congenital defects or abnormalities
  3. Infants whose mother had pregnancy-related conditions such as gestational hypertension, pre-eclampsia or eclampsia, gestational diabetes, cholestasis of pregnancy, or other high-risk obstetric factors, as well as a history of alcohol or drug abuse during pregnancy
  4. Infants who have used antibiotics within 2 weeks prior to enrollment
  5. Infants who have had specific diseases affecting growth and development within 1 month prior to enrollment (e.g., pneumonia, severe diarrhea, severe constipation, severe cow's milk protein allergy, malnutrition, gastrointestinal surgery, severe congenital heart disease, epilepsy, cerebral palsy, developmental delay, confirmed genetic metabolic disorders, chromosomal disorders, genetic diseases, etc.)
  6. Infants with severe primary diseases affecting other important organs or systems such as the heart, liver, kidney, hematopoietic system, etc.
  7. Infants who have used investigational drugs or participated in other clinical studies before screening
  8. Infants who have consumed probiotic products within 1 month prior to enrollment (calculated from birth to enrollment for infants aged <1 month)
  9. Infants who have used immunosuppressive drugs (such as glucocorticoids, immunosuppressants) before enrollment
  10. Infants with known allergies to the ingredients of probiotic products
  11. Children who require hospitalization for treatment due to malnutrition
  12. Other reasons that researchers consider as unsuitable for participation in the clinical trial, such as those that could affect efficacy evaluation or individuals with poor compliance

Infants and young children aged 6-12 months with good health

1. Infants who have used antibiotics within 2 weeks prior to enrollment
2. Infants who have had specific diseases affecting growth and development within the 1 month prior to enrollment (Infants who have had specific diseases affecting growth and development within 1 month prior to enrollment (e.g., pneumonia, severe diarrhea, severe constipation, severe cow's milk protein allergy, malnutrition, gastrointestinal surgery, severe congenital heart disease, epilepsy, cerebral palsy, developmental delay, confirmed genetic metabolic disorders, chromosomal disorders, genetic diseases, etc.)
3. Infants with severe primary diseases affecting other important organs or systems such as the heart, liver, kidney, hematopoietic system, etc.
4. Infants who have used investigational drugs or participated in other clinical studies within 3 months prior to screening
5. Infants who have consumed probiotic products within 1 month prior to enrollment
6. Infants who have used immunosuppressive drugs (such as glucocorticoids, immunosuppressants) before enrollment
7. Infants with known allergies to the ingredients of probiotic products
8. Children who require hospitalization for treatment due to malnutrition
9. Other reasons that researchers consider as unsuitable for participation in the clinical trial, such as those that could affect efficacy evaluation or individuals with poor compliance

Infants and young children aged 12-36 months with good health

1. Infants who have used antibiotics within 2 weeks prior to enrollment
2. Infants who have had specific diseases affecting growth and development within the 1 month prior to enrollment, such as pneumonia, severe diarrhea, severe constipation, severe cow's milk protein allergy, malnutrition, gastrointestinal surgery, severe congenital heart disease, epilepsy, cerebral palsy, developmental delay, confirmed genetic metabolic disorders, chromosomal disorders, genetic diseases, etc.
3. Infants with severe primary diseases affecting other important organs or systems such as the heart, liver, kidney, hematopoietic system, etc.
4. Infants who have used investigational drugs or participated in other clinical studies within 3 months prior to screening
5. Infants who have consumed probiotic products within 1 month prior to enrollment
6. Infants who have used immunosuppressive drugs (such as glucocorticoids, immunosuppressants) before enrollment
7. Infants with known allergies to the ingredients of probiotic products
8. Children who require hospitalization for treatment due to malnutrition
9. Other reasons that researchers consider as unsuitable for participation in the clinical trial, such as those that could affect efficacy evaluation or individuals with poor compliance