Edit in JSFiddle

function ObjectCellRenderer() {
}

ObjectCellRenderer.prototype.init = function (params) {
    this.span = document.createElement('span');
    this.span.title=''
    this.span.innerHTML='';
    this.refresh(params)
};

ObjectCellRenderer.prototype.refresh = function(params) {
    var res = ''
    if(params.value) {
        for(var i=0;i<params.fields.length;i++) {
            res += params.fields[i].label + ': ';
            res+=params.value[params.fields[i].name] + ' ';
        }
    }
    
    this.span.innerHTML=res;
}

ObjectCellRenderer.prototype.getGui = function () {
    return this.span;
};


function ObjectEditor() {
    
}

var onKeyDown = function(event) {
        var key = event.which || event.keyCode;
        if (key == 37 ||  // left
            key == 39 || // right
            key == 9 ) {  // tab
            event.stopPropagation();
        }
    }

ObjectEditor.prototype.init = function (params) {
    this.container = document.createElement('div');
    this.container.style = "border-radius: 15px; border: 1px solid grey;background: #e6e6e6;padding: 10px; ";
    this.container.onkeydown = onKeyDown
    
    for(i=0;i<params.fields.length;i++) {
        var field = params.fields[i];
        var label = document.createElement('label');
				label.innerHTML = field.label+': ';
        var input = document.createElement('input');
        input.name = field.name;
        if (params.value) {
        	input.value = params.value[field.name]; 
        }
        
        this.container.appendChild(label);
        this.container.appendChild(input);
        this.container.appendChild(document.createElement('br'));
    }
    
    var saveButton = document.createElement('button');
    saveButton.appendChild(document.createTextNode('Ok'))
    saveButton.addEventListener('click', function (event) {
        params.stopEditing();
    });
    this.container.appendChild(saveButton);
};

ObjectEditor.prototype.getGui = function () {
    return this.container;
};

ObjectEditor.prototype.afterGuiAttached = function () {
    var inputs = this.container.getElementsByTagName('input');
    inputs[0].focus();    
};

ObjectEditor.prototype.getValue = function () {
    var res = {};
    var inputs = this.container.getElementsByTagName('input');
    for(j=0;j<inputs.length;j++) {
          res[inputs[j].name] = inputs[j].value.replace(/^\s+|\s+$/g, "");
    }
    return res;
};

ObjectEditor.prototype.destroy = function () {
};

ObjectEditor.prototype.isPopup = function () {
    return true;
};


function MultiLineCellRenderer() {
}

MultiLineCellRenderer.prototype.init = function (params) {
    this.span = document.createElement('span');
    this.span.title=''
    this.span.innerHTML='';
    this.refresh(params);
}    

MultiLineCellRenderer.prototype.refresh = function (params) {
    if (params.value === "" || params.value === undefined || params.value === null) {
        this.span.innerHTML = '0 items';
    } else {
        var res = ''
        for(var i=0;i<params.value.length;i++) {
            res += (i+1)+': ' + params.value[i] 
            res+='\n';
        }
        this.span.title = res;
        this.span.innerHTML = params.value.length + ' item' + (params.value.length==1?"":"s");
    }
};

MultiLineCellRenderer.prototype.getGui = function () {
    return this.span;
};

function MultiLineEditor() {}

MultiLineEditor.prototype.onKeyDown = function (event) {
    var key = event.which || event.keyCode;
    if (key == 37 ||  // left
        key == 39 || // right
        key == 9 ) {  // tab
        event.stopPropagation();
    }
};

MultiLineEditor.prototype.addLine = function(val) {
    var li = document.createElement('li');
    var span = document.createElement('span');
    var removeButton = document.createElement('button');
    removeButton.style='margin-left: 5px; text-align: right; '
    removeButton.innerHTML = 'Remove'
    span.innerHTML = val;
    li.appendChild(span)
    li.appendChild(removeButton)
    
    this.ul.appendChild(li);
    var that = this;
    removeButton.addEventListener('click', function(event) {
        that.ul.removeChild(this.parentElement);
    });
}

MultiLineEditor.prototype.init = function (params) {
    var that = this;
    this.container = document.createElement('div');
    this.container.style = "border-radius: 15px; border: 1px solid grey;background: #e6e6e6;padding: 10px;";
    
    this.ul = document.createElement('ol');
    if (params.value) {
        for(i=0;i<params.value.length;i++) {
            this.addLine(params.value[i]);
        }
    }
    this.container.appendChild(this.ul);
    this.input = document.createElement('input');    
    this.container.appendChild(this.input);
    
    this.addButton = document.createElement('button');    
    this.addButton.innerHTML = 'Add';
    this.addButton.addEventListener('click', function (event) {
        var val = that.input.value;
        if(!val || val==undefined || val=='') return;
        that.addLine(val, that.ul);
        that.input.value='';
    });
    this.container.appendChild(this.addButton);
    
    this.saveButton = document.createElement('button');
    this.saveButton.innerHTML = 'Ok';
    this.saveButton.addEventListener('click', function (event) {
        params.stopEditing();
    });
    this.container.appendChild(this.saveButton);
    
};

MultiLineEditor.prototype.getGui = function () {
    return this.container;
};

MultiLineEditor.prototype.afterGuiAttached = function () {
    var inputs = this.container.getElementsByTagName('input');
    inputs[0].focus();
};

MultiLineEditor.prototype.getValue = function () {
    var res = [];
    for(var i=0;i<this.ul.children.length;i++) {
        res.push(this.ul.children[i].children[0].innerHTML);
    }
    return res;
};

MultiLineEditor.prototype.destroy = function () {
};

MultiLineEditor.prototype.isPopup = function () {
    return true;
};

var addressFields = [
	{'name': 'address', 'label': 'Address' },
  {'name': 'zip', 'label': 'ZIP' },
  {'name': 'city', 'label': 'City' },
]

var columns = [
    {
        headerName: 'ID', field: 'id', width: 50, editable: true  
    }, {
        headerName: 'Name', field: 'name', width: 100, editable: true
    }, {
        headerName: "Address", field: "address", width: 200, editable: true,
        cellRenderer: ObjectCellRenderer,
        cellEditor: ObjectEditor,
        cellEditorParams: {
          fields: addressFields
        },
        cellRendererParams: {
          fields: addressFields
        }
    }, {
        headerName: "Children", field: "children", width: 200, editable: true,
        cellRenderer: MultiLineCellRenderer,
        cellEditor: MultiLineEditor
    }
];

var gridOptions = {
    columnDefs: columns,
    rowData: []
};

new agGrid.Grid(document.querySelector('#myGrid'), gridOptions);

document.querySelector('#addRow').addEventListener("click", function() {
    gridOptions.api.addItems([{}]);
});

<button id='addRow' >Add row</button>
<div id="myGrid" style="height: 500px" class="ag-blue"></div>