Hi mummy, for my LO, they have been wearing long sleeve tee and pants (not so thick) from birth to 4th mths. Especially nowadays there might be raining and mosquitoes so it will be good to cover them. Of coz if the weather is v hot, I will let them wear shorts instead of pants. But most of the times, is long.
When they are outside, it depends on where we are going and whether is indoor or outdoor. If outdoor, short sleeves. Indoor, I usually let them wear long sleeve and bring a blanket along in case, too cold.