My son is 4 months and 6.3kgs would he be able to fit the small 2.5 sleep bag?

Hi Britney, The 2.5 TOG Love to Dream sleep sack is a good option or perhaps you may like to try a Babu Merino Sleep Bag or a Woolbabe Sleep Bag and pop your wee one in a long sleeved bodysuit or top to keep his arms warm. If you have any other questions please don’t hesitate to email or call your nearest store: https://www.babyonthemove.co.nz/store-locations/