破烂儿 is colloquial Beijing-flavored speech — the
儿 suffix (érhuà) tags it as casual.
捡破烂儿 ('to pick through junk', for scrap dealers/scavengers) and
收破烂儿 ('to collect junk', the cry of the recyclable-buyer roaming alleys) are everyday neighborhood phrases. The non-érhuà form
破烂 carries the same meaning more neutrally.