childOptions (childOptions) {
        if (!arguments.length) {
            return this._childOptions;
        }
        this._childOptions = childOptions;
        this._children.forEach(child => {
            child.options(this._childOptions);
        });
        return this;
    }
Get or set chart-specific options for all child charts. This is equivalent to calling
{@link BaseMixin#options .options} on each child chart.
@param {Object} [childOptions]
@returns {Object|CompositeChart}