<?php
if (!empty($_POST[Fname2])) // if "not empty isn't working, try a combination of [man]isset[/man]() and [man]strlen[/man]()
{
echo "Enfant 2:";
echo "Prénom et nom:";
echo $_POST['Fname2'];
echo $_POST['Lname2'];
echo "Allergies connues :";
echo $_POST['Allergies2'];
echo "Date de naissance:";
echo $_POST['DDN2'];
echo "RAMQ:";
echo $_POST['RAMQ2'];
echo "Exp.:";
echo $_POST['Exp_2'];
}
It really looks like you could use some formatting of your output, also.
You can do stuff like this (use the "dot", for concatenation) and use fewer echo() statements:
echo "Name: ".$_POST['name_variable']."<br>";