Child Theme Widgets Now Below all Content

nothing to do with the upgrade.

caused by an unclosed div in your latest post ‘Learn “Beautiful Things” by Gungor’:

edit that post, using the html setting of the post editor;
find:

Learn Guitar Songs!<br>
Artist: Gungor<br>
Album: <em>Beautiful Things</em><br>
Song: “Beautiful Things”</p>
<div style="clear: both;">
<h3>Important Notes</h3>

remove this line:

<div style="clear: both;">

also, the h1 tag of the site title is not closed properly on your front page;
edit header.php;
compare your code with this section from the unedited Twenty Ten:

<<?php echo $heading_tag; ?> id="site-title">
					<span>
						<a href="<?php echo home_url( '/' ); ?>" title="<?php echo esc_attr( get_bloginfo( 'name', 'display' ) ); ?>" rel="home"><?php bloginfo( 'name' ); ?></a>
					</span>
				</<?php echo $heading_tag; ?>>

and fix it.

the validation report reports a missing </h1> tag:

Line 64, Column 28: Unclosed element h1.

http://validator.w3.org/check?uri=http%3A%2F%2Fblog.igniteguitar.com%2F&charset=%28detect+automatically%29&doctype=Inline&group=0

which is often caused by wrong edits to that particular section in header.php;

if you would like me to check the code, you can paste the full code of header.php into a pastebin.com and post the link to it here – HOWTO

this is missing between line 90 and line 91:

</<?php echo $heading_tag; ?>>

this section should look like so:

</span>
</<?php echo $heading_tag; ?>>
<!--                            <div id="site-description"><?php bloginfo( 'description' ); ?></div> -->