Well done for observing this difference! There is definitely a marked contrast between the wild bay and the safe beach where Jerry's mother stays. For Jerry, however the "wild-looking" bay meets his need for danger and his feeling that he has to exert his independence and show his maturity by going through some kind of rite. The setting of this wild bay is incredibly important, as it is here that Jerry discovers the tunnel and decides on the challenge that he is going to set for himself. It is this desire to prove himself that causes Jerry to go to the wild bay, rather than follow his mother to the safe beach, as she would like. Thus it is that, after having gone once, we are told that "he did not ask for permission" the next day to return there and he continues to exert his independence from her throughout the rest of the tale as he prepares for his challenge.