Fledgling Wood pigeon

Hi yesterday at dusk we spotted a fledgling wood pigeon in our garden. We observed for 2 hours but sadly when we took out eyes away something ? Cat got it as when we went to look for it we found feathers and entrails. 
this morning we spotted another fledgling in the garden and observed it over the day when we spotted the mother calling for it and later feeding it. This evening again it’s sat in the garden with no sign of mum. What do we do? We don’t want to leave it as we did it’s sibling to be killed by a predictor? Thank you