Making this bib is very simple. First you just make a square, and then add the strip that goes aroung the neck.
For the final details, just make a colorful crochet border. I suggest a simple one for boys, and a lacy one for girls.

I did not write the name of the yarn, beacuse I am using a local one which is brandless. You can also use a two simple threads. You can even use other yarns; just be careful to use one that can be washed easily, as they get “dirty”.