What is Golding's purpose in introducing the scene of little ones playing in the sand and in the pool?

In my opinion, Golding does this to model that these
little ones are innocent and children. The idea of play models that they are still
developing and not capable of responsibilities that others will have to carry for them.
Innocence is demonstrated in this as well because they did not choose to be here, and
this play shows their oblivousness to the serious nature of the new situation of being
stranded on this island without adults. It is almost as if these small kids expect that
the adults will come and find them and take care of
them.

We find the beach and ocean to be calming. These
children are highly relaxed. This will certainly be contrasted later with the fears
little children are capable of possessing. The entirety of the setting contrasts with
the predicament the boys are experiencing. This moment at the pool just exaggerated
that. Read about setting in the following
link.