Methotrexate is a medication that is used to treat various types of cancer and autoimmune diseases. It is administered to children in different ways, depending on the condition being treated.

For children with cancer, methotrexate is typically given intravenously (IV) in a hospital setting. The dose and frequency of administration depend on the type of cancer and the child's weight. The drug is usually given in combination with other chemotherapy drugs, and the treatment plan is determined by the child's oncologist [1].

For children with autoimmune diseases such as juvenile idiopathic arthritis (JIA), methotrexate is given orally once a week. The dose is based on the child's weight, and the medication can be taken with or without food. The child's response to the medication is closely monitored, and the dose may be adjusted over time [2].

In some cases, methotrexate may be given subcutaneously (under the skin) to children with autoimmune diseases. This method of administration may be preferred for children who have difficulty swallowing pills or who experience gastrointestinal side effects from the oral medication. Subcutaneous injections are typically given once a week, and the dose is adjusted based on the child's weight and response to the medication [3].

Overall, the method of administration for methotrexate in children depends on the condition being treated and the child's individual needs. The medication is usually given under close medical supervision to ensure its safety and effectiveness.

Sources:
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5153332/
[2] https://pubmed.ncbi.nlm.nih.gov/20149329/
[3] https://www.drugpatentwatch.com/p/tradename/METHOTREXATE