Beginning-sound work should start with listening. Children do not need to read a word to hear that sun and sock begin in the same way. Clear pictures let them focus on the sound relationship.
Say the whole word naturally
Name each picture together, then stretch only the first sound once. Avoid adding an extra vowel sound to consonants; say mmm rather than muh.
Compare two choices
If the task is difficult, offer two pictures and repeat their names. Ask which word starts like the target. Gradually return to the full set.
Extend beyond the page
Look for another object in the room with the same beginning sound or invite the child to draw one. This checks whether the idea transfers to new examples.