How to format DatePicker date to dd/mm/yyyy so that it displays correctly in the form field and is validated correctly?

I understand that MySQL stores date in Y-m-d H:i:s format. However, I want to generate dates based on dd/mm/yyyy and display in this format in the form field once the date is picked (and validated as dd/mm/yyyy). Unfortunately, it doesn't work. I tried all the methods described in the other threads but still can't get it work. I experimented with different permutations and ended up getting invalid format warning, incorrect format or 1/1/1970.

Can you advise what I should do? I have run out of idea how to make this work. Here are the codes in questioned:

DatePicker...
$(function(){
$('#session_date_start').datepicker({
changeMonth: true,
changeYear: true,
dateformat: "dd/mm/yy",
onClose: closeDatePicker_session_date_start
});

Form Field...
<input id="session_date_start" name="session_date_start" type="text" value="<?php echo((isset($_GET["invalid"])?ValidatedField("sessionupdate","session_date_start"):"".(($row_WADAsession["session_date_start"])?date("d/m/Y",strtotime($row_WADAsession["session_date_start"])):"")."")); ?>" class="formTextfield_Medium" tabindex="4" onBlur="hideServerError('session_date_start_ServerError');">
});

Spry Validation...
var session_date_start_Spry = new Spry.Widget.ValidationTextField("session_date_start_Spry", "date",{ format:'dd/mm/yyyy' , validateOn:["blur"]});

Attached is the php file. The problematic field is: session_date_start. Once this issue is solved, I will replicate the correct formatting to the other date fields.

I have included the site address in the private message.

in the datepicker code, you have:
dateformat: "dd/mm/yy",

this is not valid, the f needs to be capitolized:
dateFormat: "dd/mm/yy",

It doesn't fix the issue even after I capitalized dateFormat. I just tried updating record ID 3 (Email Marketing) using dateFormat but ended up getting 1 Jan 1970. Actually, I have been using dateFormat with capital F over the last two days without success.

so the issue now not that it is not passing validation, but what is being stored in the database, right?

in the update behavior, the code has to reformat the date to be compatible with MySQL. it uses the date and strtotime function refomat the date to yyyy-mm-dd H:i:s format:

date("Y-m-d H:i:s", strtotime($_POST["session_date_start"]))


the problem with this is that the strtotime function uses the separator to determine if the data uses the US Format or the UK format. From the php web site:
http://php.net/manual/en/function.strtotime.php

  Note:
Dates in the m/d/y or d-m-y formats are disambiguated by looking at the separator between the various components: if the separator is a slash (/), then the American m/d/y is assumed; whereas if the separator is a dash (-) or a dot (.), then the European d-m-y format is assumed.  

When the separator uses a slash, strtotime assumes the US m/d/y format, but you are passing it as d/m/y

one of 2 way to fix it:
1) Use the dash separator instead

2) add code at line one of your page to convert the slash to a dash
<?php if(isset($_POST["session_date_start"])) $_POST["session_date_start"] = str_replace("/","-",$_POST["session_date_start"]); ?>

It works now. Thanks for the help!

One more thing, is it possible to display the date in my form as say 11 Dec 2014 rather than 11/12/2014? Meaning, when the form loads, it pre-populates the text field with the date from the recordset in 11 Dec 2014. Then when I pick a date from the picker, it can also display in the same format. When the form submits, it will send the date according to MySQL's format.

No, the date picker does not support that date format.