Head collars are paired with verbal cues or physical gestures.
e.i. when they walk beside you say "good heel" . Using the association of them walking beside you and praise. Like I said it's not meant to be a crutch, it should be paired with praise for the alternative behavior. Dogs are smart and will clue in, hey when I do this my owner likes it and I get pets/treats/toys, whatever.
Prongs do work on stronger pulling dogs and larger dogs who are VERY calm but just pull, usually over 100 lbs too, because people usually cannot physically restrain a 100 lb pulling dog. But as a trainer I've seen too many dogs have prong collars and have become aggressive and have negative associations with them. If you pull back if the dog is pulling at a kid, that pinch could send a wrong message association pain=child and can become aggressive to avoid having that negative feeling.