1/2″ Buttons

I'm sewing 4 Library Dresses, in 21 wale Kaufman corduroy, for my granddaughters for Christmas. The sizes are 12/18 mo, 6, 7 and 12. The pattern calls for 1/2" buttons. I ordered the buttons and they measure 1/2" but they look small. I'm concerned if they will hold the entire back of the dresses closed?