RobH_en_tn/heb/05/13.md

takes milk

Here "takes" stands for "drinks." Alternate translation: "drinks milk" (See: rc://en/ta/man/translate/figs-metonymy)

because he is still a little child

Spiritual maturity is compared with the kind of food that a growing child eats. Solid food is not for a tiny baby, and that is a figure describing a young Christian who only learns simple truths; but later, more solid food is given to the little child, just as when a person matures he can learn about matters that are more difficult. (See: rc://en/ta/man/translate/figs-metaphor)