bricks and pebbles.
'bata' from Kamus Besar Bahasa Indonesia:
tanah liat yg diaduk sampai halus, kemudian dicetak, dikeringkan, lalu dibakar (dipakai untuk membuat dinding dsb); batu bata;
bata from Oxford English Dictionary:
A substance formed of clay, kneaded, moulded, and hardened by baking with fire, or in warm countries and ancient times by drying in the sun; used instead of stone as a building material.
batu kali from KBBI:
n. (entry = batu)
-- kali batu dr sungai; batu air;
a small stone made smooth and round by the action of water or sand
judging from the definitions and context, i say the my answer is appropriate.
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Native speaker of: English, Indonesian