select ROW(qid::integer,a.prev_qid::integer) ids from getchildren(39) b
    cross join lateral(select qid prev_qid from getprevquestion(b.qid)
        )a

(42,39)
(43,39)
(48,42)
(49,42)
(50,42)
(51,43)
(52,43)
(53,43)

((42,39),(43,39),(48,42),(49,42),(50,42),(51,43),(52,43),(53,43))

select array_agg(ids) from (
select ROW(qid::integer,a.prev_qid::integer) ids from getchildren(39) b
    cross join lateral(select qid prev_qid from getprevquestion(b.qid)
        )a
    )b