Expected:

Actual:

<script src="https://cdn.botframework.com/botframework-webchat/latest/webchat.js"></script>
Input.Date fields in Adaptive Cards have a value property that is supposed to specify the input's initial value. While the property works in Microsoft Teams, it seems to be ignored in Web Chat.
{
"type": "AdaptiveCard",
"body": [
{
"type": "Input.Date",
"id": "id-date12",
"value": "12/13/14"
}
],
"actions": [
{
"type": "Action.Submit",
"title": "Submit"
}
],
"$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
"version": "1.0"
}
The value properties of other input fields seem to work correctly.
[Bug]

It looks like it's not respected on Adaptive Cards either.
I think this is related to https://github.com/microsoft/BotFramework-WebChat/issues/2192
~I would file this with Adaptive Cards.~ Nevermind, please see below.
After some further investigation, I have discovered that the value property does work if you provide the date in the format yyyy-mm-dd. It does not work in the format mm/dd/yy, though that seems to be a Web Chat specific problem.
I have also discovered another bug while testing this. The placeholder property does not work in Input.Date though it does work in Input.Text. The placeholder property works for both input types in Microsoft Teams. The placeholder property was introduced in Adaptive Cards 1.0 so this can't be a version issue.
This is HTML issue.
value attribute is not in the format of yyyy-mm-dd, Chrome/Edge will not be able to parse it. Not Adaptive Cards or Web Chat issue. You can try it out at https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/date.placeholder attribute is not supported. Excerpt below:
Looks like @corinagum opened an issue for the date input placeholder issue in the Adaptive Cards repo already https://github.com/microsoft/AdaptiveCards/issues/2255