The under-representation of children in COVID-19 disease goes hand in hand with the absence of predictors of severe Covid-19 in children. Indeed, if children are at risk of infection similar to adults in general, less are likely to present or have presented until now, severe symptoms.

Lymphopenia is one of the important markers. But seen less in children and are protected.

Several factors may contribute to COVID-19 associated lymphopenia. Lymphocytes express the ACE2 receptor on their surface; therefore, SARS-CoV-2 may directly infect those cells and ultimately lead to their lysis. Furthermore, the cytokine storm causing markedly elevated levels of interleukins and tumor necrosis factor (TNF)-α, may promote lymphocyte apoptosis. The cytokine activation may be associated with atrophy of lymphoid organs, including the spleen, and can further impair lymphocyte turnover. Coexisting lactic acid acidosis may also inhibit lymphocyte proliferation. Decreased lymphopenia in children maybe again due to immaturity and less ACE 2 receptor in children

This paper looks into the question but from a similar perspective to what Dr Nirmal Mohakud expressed above:

Article Diagnosis of COVID-19 in children: the story evolves

The under-representation of children in COVID-19 disease goes hand in hand with the absence of predictors of severe Covid-19 in children. Indeed, if children are at risk of infection similar to adults in general, less are likely to present or have presented until now, severe symptoms.

Several infections appeared in Erbil and Baghdad among children aged one month, one year and two years, with COVID-19, but no deaths were recorded.