Q: before felting: approx. 40 cm
A: Before felting: approx. 40 cm

Q: also, instead of the in keyword one can introduce a new operator specifically all. check out its semantics (meaning).
A: Also, instead of the IN keyword one can introduce a new Operator specifically ALL. Check out its semantics (meaning).

Q: let us use our intelligence and learn these meanings...
A: Let us use our intelligence and learn these meanings...

Q: a child soldier is a child who is under 18 and who are directly or indirectly involved in an armed conflict as part of an armed group.
A:
A child soldier is a child who is under 18 and who are directly or indirectly involved in an armed conflict as part of an armed group.