Hi, Massimiliano, notice the two cases are somewhat different:
"As a child, I would steal candy."
"As a child, I [used to habitually] steal candy."
—used in auxiliary function to express custom or habitual action (www.m-w.com)
"I knew you would say that."
"I believed in the past, 'you WILL say that at a later time'."
—used in auxiliary function to express plan or intention (www.m-w.com)