Background: To examine the hypothesis that ACE2 and TMPRSS2 expression are related to disease susceptibility and severity across age groups and to evaluate the role children play in the household transmission of SARS-CoV-2.Methods: We used a combined serological strategy to confirm past infection in subjects diagnosed with COVID-19 between march 10th and June 2nd 2020 and to evaluate their household members. We also quantified ACE2 and TPMRSS2 expression from saliva. A total of 258 households were included in the study, for a total of 650 volunteers (including 89 children aged under 18 years of age).Results: Our combined testing strategy increased our sensibility by 10%. Antibody indexes decreased with age in children and increased with age in adults. They also increased with disease severity. ACE2 expression was slightly increased in younger children. ACE2 was not related to any other factors. We did not find any relationship between TMPRSS2 expression and any of the studied factors. Children are less frequently infected by SARS-CoV-2 (OR=0,56), they present fewer symptoms and decreased severity. Age and sharing the bedroom with an index case increases the risk of acquiring the infection. The risk in adults increases with age, whereas in children, it increases in younger children. Conclusions: Our results do not support that the level of expression of ACE2 and TMPRSS2 might be related to susceptibility or severity of COVID19 disease. Children have a decreased susceptibility to SARS-CoV-2 infection compared to adults and, when infected, they present less symptoms and a more benign course.