four children lay on a tube.
The people are younger than 21.
Four children are people younger than 21.
exists e1 x1 x2.(on(e1,x2) & n_tube(x2) & Actor(e1,x1) & v_lay(e1) & n_child(x1) & card_eq_4(x1))
exists p1 x1.(n_people(x1) & exists x2 x3.((x1 = x2) & than(x2,x3) & n_date(x3) & a_date_day_21(x3) & a_date_day_21(x3) & n_younger(x2)))