let arr1 = [
   {id = 1,
   name = "Anna"},

   {id = 2,
   name = "Chris"}
   ]

   let arr2 = [
   {childName = "Brian",
   {source = 1}},
   {childName = "Connie",
   {source = 2}}
   {childName = "Dory",
   {source = 1}}
   ]

arr1.forEach(el => el.children = arr2.filter(checkMatch));

            function checkMatch(child){
                for(let i=0;i<arr1.length;i++){
                    child.childName.source === arr1[i].id
                }
            }