Agregar al objeto json php
<?php
$arr = '[
{
"id":1,
"name":"Charlie"
},
{
"id":2,
"name":"Brown"
},
{
"id":3,
"name":"Subitem",
"children":[
{
"id":4,
"name":"Alfa"
},
{
"id":5,
"name":"Bravo"
}
]
},
{
"id":8,
"name":"James"
}
]';
$arr = json_decode($arr, TRUE);
$arr[] = ['id' => '9999', 'name' => 'Name'];
$json = json_encode($arr);
echo '<pre>';
print_r($json);
echo '</pre>';
Strange Salamander