Only people who are symptomatic or sick should be tested. It can be challenging to decide if your child has symptoms. The symptoms of Lyme disease vary so much. There may be a tendency to over analyze things that are normal or ignore things that are abnormal. Whereas some parents are dismissive of symptoms, others may be overly paranoid. A child may have ADD. If it runs in the family then no further evaluation is required. If it atypical: it comes on later in childhood and seems to be progressive and there is no family history, then Lyme should be in the differential list of possibilities. Psychiatric and neurological symptoms do occur more frequently in children with Lyme disease. I have seen learning disabilities, tics, mood swings. anxiety, depression, OCD behavior and other neurological symptoms improve when Lyme is treated. Kids should not complain of joint pain and excessive fatigue. There is probably no such thing as "growing pains."
This would affect bones and muscles, not joints, if it were to occur. Children without symptoms should never be tested. Remember two things: testing is very difficult, controversial, and unreliable, and when patients are treated for Lyme disease, the treatment is continued until symptoms resolve. Someone who is without symptoms should not be treated no matter what the tests show. There is no way to prevent the appearance of future symptoms by treating a positive test. So testing people without symptoms is without benefit and could be potentially harmful if children are treated when it is not appropriate.