Load child nodes without expanding parent node

How to load child nodes for the parent node without expanding it?
I have checkbox column in the grid. When user checks the checkbox on the node, I need to load and check all child nodes. I don’t need to expand the checked node until user manually clicks expand button.

Unfortunately you need to expand the row.
You may try to expand it, check the nest rows and then collapse that row back using the API:
docs.dhtmlx.com/api__dhtmlxtreeg … nitem.html
docs.dhtmlx.com/api__dhtmlxtreeg … eitem.html