Just back from OZ flew with an 17mth old and 6 year old. Went with Malaysian airlines- very good except basonette too small- think same on each airline. Nightmare flying with child that will not sit still and wants to wander around when everyone else is sleeping- I am sure yours is better behaved.
Stopped in Singapore way out 2 days, nice place, safe, airport only 25 mins from centre- taxis cheap, clarke quay was great place to stay- expensive enough there.
Stayed in KL on way back - airport an hour from city haggle for everything, shopping was good esp in chinatown, good hotel was cheap just booked it a couple a of weeks before hand to get better rate €50 a night including breakfast. Traffic is mad there!
Both are very hot and humid, more life to KL then Singapore - I prefer KL, missus prefers Singapore so not sure if helps- prob easier to get around Singapore with a child.