Possible to have password for iPad mail?

No. To tell Apple you want this, go here:

http://www.apple.com/feedback/ipad.html

As an alternative until a better solution comes along, before you hand the iPad to the grandkids, go into the settings on your ipad and then go into the mail settings and turn the account switch to OFF on your mail account. This will temporarily hide your email account and your emails. They would really have to intentionally navigate to the settings to turn it back on to get to your email. When you get the ipad back from the kids, you can turn it back on yourself and everything will be as you left it. Hope that makes sense.

Go to settings... Mail, contacts and calendar, remove you password for you email account.

It's been said several times before, but the iPad needs Multi-user accounts in my opinion.
In a family environment it's a multi-user device and email privacy, constantly logging in/out to Facebook, Twitter, forums, eBay, etc. is a right royal pain.
The fact that Apple won't allow access to me.com webmail on the iPad makes the email issue even more difficult.
(Yes, I have sent feedback on this some time ago.)

David M Brewer wrote:
Go to settings... Mail, contacts and calendar, remove you password for you email account.

This won't work, the mail settings need to confirm a password so it won't let you confirm unless you have a password and if it is a fake password, it won't confirm either. Even if you could delete the password and you had previously downloaded mail on your iPad, the mail will still be accessible. I would just stick with turning off the particular mail account using the ON/OFF switch in settings as I posted. This will cause all your info to temporarily disappear in the mail app so your grandkids won't see it if they go into the mail app. You can easily turn it back on later. Good luck.

I don't have my iPad here but I know you can hide and restrict some things. Anyone know
if that works with email?

In the iPad's setting section there is a restrictions portion that can allow/restrict use of specific applications but Mail is not one of them.

You are most welcome and I hope you have a wonderful day with your WONDERFUL iPad! :O)

I sent a request to apple as well!