Here’s how you add children at any index of a scroll box. Re-create this function in a blueprint library so that you can reuse it in any widget:
(L_WidgetsArray is a local variable in the function of the ‘widget object reference’ type)
This function will take a scroll box as an input and save all of its children in a temporary local array variable called L_WidgetsArray. It will then insert the input child widget into the temporary array at the specified input index. It will then clear all the children in the input scroll box and add all the children to it from L_WidgetsArray which now contains your child widget inserted into it.
To add the child all the way at the end of the scroll box, you need to get the last index which you can get using the ‘Get Children Count’ node.