Can those of us who have POA sign the stimulus Visa card for LO we're caring for?

I didn't have to sign mine. It was good at any ATM, and for myself I had them deposit to money in my account. They will ask YOU how much you got on the card as the monitors they plug it into don't tell the amount, so listen carefully when you they tell you on the phone when you "activate" the card, to the amount you are getting. For those with higher income it isn't the 600.00 amount. So just go to your bank teller and have them put the card right in their machine. Mine didn't ask for a signature at all. When you activate it with the SS number on the phone that will take care of everything.

The FAQ at the EIP card site that disgustedtoo mentioned also explains the remote deposit options:

"There are multiple ways to transfer the funds

1 from your EIP Card to an existing bank account at no cost to you. You will need the Routing and Account number for your bank account to complete the transfer.
Transfer funds online at EIPCard.com
Be sure you have activated your EIP Card before attempting to transfer funds.
Register for online access by going to EIPCard.com and click on “Login” and “Register Now”. Follow the steps to create your User ID and Password. Be sure to have your EIP Card handy.
Select “Transfers in U.S.” under Money Out.
Follow the steps to set up your destination bank account prior to completing your ACH transfer.
Transfers should post to your bank account in 2-3 business days.

Transfer funds using the Money Network Mobile App
Be sure you have activated your EIP Card before attempting to transfer funds.
Download the Money Network Mobile App2 and register for mobile access by clicking “New User?”. Follow the steps to create your User ID and Password. Be sure to have your EIP Card handy.
Click the top left menu and click “Send Money to an External Bank Account” under Move Money Out.
Follow the steps to set up your destination bank account prior to completing your ACH transfer.
Transfers should post to your bank account in 2-3 business days.

Transfer funds by calling 1.800.240.8100
Be sure you have activated your EIP Card before attempting to transfer funds.
Call 1.800.240.8100 and follow the prompts to authenticate with the Interactive Voice Response Unit (IVRU).
Once authenticated by the IVRU, follow the prompts to set up your destination bank account prior to completing your ACH transfer.
Transfers should post to your bank account in 2-3 business days.

ACH Transfer to Domestic Bank Limits Apply: $2,500 per transaction | $2,500 per day | $5,000 per month. Please see your Cardholder Agreement online at EIPCard.com"

https://www.consumer.ftc.gov/blog/2020/05/what-know-about-economic-impact-payment-debit-cards

This page doesn't answer the question, but it does give the phone number to activate the card and the same number if you have questions. Perhaps they can answer the questions?

I should think once the card is activated, you can use POA to deposit it into their account, which you already have POA for.

Another option, see https://www.eipcard.com/

There is a link on this page for a cardholder agreement - it's about the closest answer there might be:

"Each time you use your Card, you represent and warrant to us that you are either the Cardholder or an authorized user of the Card. If you permit someone else to use your Card, we will treat this as if you have authorized such use and you will be responsible for any transactions made subject to such use."

YOU would be the authorized user in this case. There is also an ATM locator link, using zip code. I tried mine and there were many locations listed.

Once you activate the card and have the PIN, why worry about a signature if you just want to withdraw the cash and deposit it into the LOs account? Just go to the ATM and withdraw the cash (or as much as the ATM allows) then deposit it. You should also be able to use it if you buy something at a store using the card reader. In general, no one checks the cards/signatures anymore.

Most of my most recent CCs haven't been signed, but the card reader takes them! Not a good practice, but... In your case, I'd probably sign it with my name, followed by DPOA.