We present structural and magnetization measurements in large-grain ceramic samples of the family (La_yPr_1-y)_0.5Ca_0.5MnO₃ with y=0, 0.15, 0.3, 0.5, 0.7, 0.85 and 1.0. In this series, a change of the ionic radius in site A (r_A) modifies the structural parameters, which strongly affect the physical properties of these compounds. While the Néel temperature remains essentially constant through the series, the ferromagnetic (FM) critical temperature (T_C) decreases rapidly and the charge-order (CO) temperature (T_CO) increases on decreasing y. The crossover of T_C and T_CO determines a critical tolerance factor (t_c≈0.975) consistent with previous reports on other systems with the same Mn³⁺/Mn⁴⁺ ratio. For tolerance factors t near t_c we observe coexistence of a FM and CO phases of varying degrees depending on y. For y ≤ 0.15 we find no evidence of ferromagnetism.