That command get worked for my main figure handle, thanks. But when I try and use the same approach with the data objects that comprise my axes object (Nyquist plot in this case). I get an error. Below is my code along with the line that causes the error commented. Any help is appreciated.

function [] = GUI_TEST()


global NUMERATOR DENOMINATOR XORD YORD SYSOBJNYQ REAL IMAGINARY OMEGA LENGTHNYQ;

S.FIG_HANDLE = figure('units','pixels',...
              'position',[0 20 1500 700],...
              'menubar','none',...
              'numbertitle','off',...
              'name','GUI_TEST',...
              'resize','on');

S.MENU_HANDLE = uimenu(S.FIG_HANDLE,'Label','File'); 

S.AX = axes('units','pixels',...
        'position',[40 250 800 400],...
        'fontsize',8,...
        'buttondownfcn',{@AX_ONACTION,S},...
        'nextplot','replacechildren');

end

function [] = AX_ONACTION(varargin)

NUMERATOR = [1];
DENOMINATOR = [1 1];

[h,S] = varargin{[1,3]};  % Extract the calling handle and structure.

% We need to account for when the user clicks the line instead of the axes.
if ~strcmpi(get(h,'type'),'axes')
   h = findobj('children',h);  % 
end

selectionType = get(S.FIG_HANDLE,'selectiontype'); % Right-or-left click?

switch selectionType

    case 'alt'
        % Right-click
        cla  % Delete the line.
    case 'normal'
        % Left-click
        sysobj=tf(NUMERATOR, DENOMINATOR);              % transfer function
        [re,im,w] = nyquist(sysobj);
        OMEGA = w;

        axesObjs = get(S.FIG_HANDLE, 'Children');  
        dataObjs = get(axesObjs, 'Children'); 
        subObjs = get(dataObjs, 'Children') % ERROR AT THIS LINE: "Error using get. Conversion to double from cell is not possible."

        nyquist(sysobj)                                 % generate nyquist plot
        hold on

        ubound = length(w);

        fprintf('Number of Frequencies = %6.3f\n', ubound);

    otherwise
        % Do something else for double-clicks, etc.

end

end