To determine whether a child has been infected with syphilis, you can use syphilis serologic test, syphilis spirochete IgM antibody test, molecular biology test, and dark-field microscopy as follows: 1. Non-syphilis spirochete serologic test: Children infected with syphilis are usually positive for this test. In the case of fetal syphilis, the child is considered to be infected with syphilis if the antibody titer is 4 times or more than that of the mother, or if the titer shows an increasing trend over a 3-month follow-up period. It should be noted that autoimmune diseases may cause false-positive results of this test, so it is necessary to combine with other tests to make a comprehensive judgment. 2. Syphilis spirochete serology test: children infected with syphilis usually show positive IgM antibody, which is a kind of immunoglobulin and has high sensitivity to diagnose syphilis and can be used for early diagnosis. Usually children with positive IgM antibody can help to confirm the diagnosis of syphilis, but negative can not rule out the infection of syphilis, need to be combined with other tests to make a comprehensive judgment. 3. Molecular biology testing: molecular biology testing is the use of PCR technology for the specific detection of syphilis, this testing method not only requires good testing conditions, but also requires a wealth of technical experience in testing. 4. Dark-field microscopy: children infected with syphilis can usually be detected in the skin lesions after scraping, but negative does not mean that the child does not suffer from syphilis, but also need to be combined with other tests to determine the synthesis. For children suspected of being infected with syphilis, parents are advised to bring their children to regular hospitals for examination and standardized treatment under the guidance of professional doctors after a clear diagnosis.