The children are near a large pile of sand that is next to the water.
The children are at the beach.
Just because the pile of sand is next to water does not mean the children are at the beach.
exists p1 x1 x5.(n_water(x5) & n_child(x1) & exists s1 s2 x2 x3 x4.(near(x1,x2) & of(x2,x3) & to(s2,x5) & Theme(s2,x4) & a_next(s2) & (x3 = x4) & n_sand(x3) & n_pile(x2) & a_large(s1) & Theme(s1,x2)))
exists p1 x1 x2.(n_beach(x2) & n_child(x1) & at(x1,x2))