Are are children with underlying health conditions at risk for developing severe infection?

Depends: There are a multitude of differing health conditions, from an isolated clubfoot to cystic fibrosis. Some may be at more risk than others. If you have a specific condition in mind start over & post a question about it. Space for a response on this forum is limited so a clear specific question about a single issue is more appropriate than broad open ended posts.

Yes: Children with immune deficiency or on treatment with immunosuppressives, underlying lung or heart disease are at greater risk from infections, including Covod-19.