Agreed, age of chicks is important too.
Personally, I would not use candles, risk of fire.
Hot water bottles would work.
A huddle box may work. Carboard box with some ventilation at the top, a cut out for the chicks to go inside. Lined with straw, bedding or even some fleece fabric or a couple of old towels for them to snuggle in for warmth.
20C/68F isn't extremely cold, but could be little cool for young chicks so it's best to provide a place to snuggle into to get warm and feel protected.
Personally, I would not use candles, risk of fire.
Hot water bottles would work.
A huddle box may work. Carboard box with some ventilation at the top, a cut out for the chicks to go inside. Lined with straw, bedding or even some fleece fabric or a couple of old towels for them to snuggle in for warmth.
20C/68F isn't extremely cold, but could be little cool for young chicks so it's best to provide a place to snuggle into to get warm and feel protected.