Get a property from the first child

Questions
1

Hi! I'm creating a xslt that takes one property from the page itself, and if it's not set, searches for that property in its first child...

I got this, but seems to be wrong:

<xsl:variable name="situacionGMaps">
<xsl:choose>
<xsl:when test="string($currentPage/situacionGMaps)!=''">
   <xsl:value-of select="string($currentPage/situacionGMaps)"/>
</xsl:when>
<xsl:otherwise>
   <xsl:value-of select="$currentPage/child::*[@isDoc and string(umbracoNaviHide) != '1'][0]/situacionGMaps" />
</xsl:otherwise>
</xsl:choose>
</xsl:variable>

What am I missing? (Umbraco 4.6.1)

This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/17992-get-a-property-from-the-first-child