Does the the immunizations infants and toddlers have been receiving might contribute to their resistance to covid 19?

No : Immunity antibodies created by vaccines are selective to the disease they are designed to fight off. It is apparent from most studies that kids have fared much better with covid-19 than they do to flu. Some data suggests as many as 50% or more may get the disease but never have symptoms. Variation of effect by age/gender or ethnicity are features of some diseases.