A dangerously low Lymphocyte count is any count of below 1,500 in adults and for children any Lymphocyte counts of below 3,000 is usually considered dangerous.
Children and infants have higher Lymphocyte counts than adults.
So children who have a lower than 3,000 Lymphocyte count are usually getting into the dangerously low Lymphocyte count.
When your Lymphocyte count is too low then it's called lymphocytopenia.
The lymphocytopenia occurs when your Lymphocyte count gets too low.
Most less severe cases of lymphocytopenia usually require no treatment but more severe cases of lymphocytopenia usually do require treatment.