How should this herb be brewed correctly to get a strong infusion? — Chereda herb 50gr (Chereda) Lekra-Set(chereda)

According to the card, for adults 10–15 g of the raw material is covered with a glass of boiling water, left to infuse for up to 2 hours and strained; for children – 1 tablespoon per glass of boiling water, infuse for 10 minutes, strain. How to make the infusion “stronger”, the card does not say; the raw material must be kept out of the reach of children.

General information (not a manufacturer's instruction): it is better to prepare the infusion fresh; take care with boiling water, especially around children.