JSFiddle - React, Tailwind, and code Playground

JavaScript

var jsono = {
    "value": 5,
    "children": [{
        "value": 18,
        "children": [{
            "value": 27,
            "children": []
        }, {
            "value": 4,
            "children": []
        }]
    }, {
        "value": 2,
        "children": []
    }]
}
var maxvalue;
JSON.stringify(jsono).match(/\"value\":\s*(\d+)/g).map(function(value){ return value.match(/(\d+)/g).map(function(value){ maxvalue =  Math.max(maxvalue || 0,value);});});
alert(maxvalue);