Final answer:
The recumbent length of a child who is less than 24 months old can be measured using an infantometer. The child should be positioned lying down on the board, and the length is read from the ruler on the board.
Step-by-step explanation:
The recumbent length of a child who is less than 24 months old can be measured by using a measuring board called an infantometer. The child is positioned lying down on the board with the head against the fixed head piece, and the movable foot piece is brought to touch the child's heels. The length is then read from the ruler on the board.
It is important to ensure that the child is calm and still during the measurement to get an accurate result.