A square has all that a rectangle needs, so every square is a rectangle. But not every rectangle is a square.
Worked example
True or false: every rectangle is a parallelogram.
Answer:True
True. A rectangle has two pairs of parallel sides.
For grown-ups: Hierarchy of 2-D figures. Below: three problems to try with the worked answers, and a free printable sheet. Children can practise the same skill as a game, with no sign-up and no ads.
CCSS 5.G.B.3–4
What this practises, for teachers
Practices hierarchy of 2-D figures (5.G.B.3–4). A printable sheet with its answer key, worked answers on the page, no accounts.