Drop a perpendicular from a point to a line — the same four steps whether the point sits on the line or above it, which is the thing worth noticing.
If they get stuck
The answer key prints on a separate page.
Swing an arc from P that crosses the line twice, then equal arcs from those two crossings; the line from P through where they meet is perpendicular to the original. It is the perpendicular-bisector construction wearing different clothes: the two crossings on the line are equidistant from P, so P is already on their bisector, and the construction just finds a second point on it.
Seeing that one construction do both jobs — a point on the line and a point off it — is the point of putting them on one sheet. A child who treats them as two separate recipes has learned twice as much as they needed to; a child who notices the arcs are the same has learned why it works.
One question off this sheet, worked a step at a time — with a sentence saying what just happened and why.
Perpendicular through a point, step by step