A girl in her pajamas is sitting on a log swing.
A girl in her pj's is playing on a swing before bedtime.
Sitting on the swing doesn't necessarily indicate she is playing on it and there is no mention that she is doing it before bedtime.
exists e1 x1 x2 x3 x4.(on(e1,x3) & n_swing(x3) & of(x3,x4) & n_log(x4) & Actor(e1,x1) & v_sit(e1) & in(x1,x2) & n_pajamas(x2) & of(x2,x1) & n_female(x1) & n_girl(x1))
exists e1 x1 x2 x3 x4 x5.(before(e1,x5) & n_bedtime(x5) & on(e1,x4) & n_swing(x4) & Actor(e1,x1) & v_play(e1) & in(x1,x2) & n_'s(x2) & of(x2,x3) & n_pj(x3) & of(x2,x1) & n_female(x1) & n_girl(x1))