Instead of buying my son a game, I would prefer to give him an amount in his Steam Wallet. Is that possible through Steam? I think I've seen Steam coupons of steam Gift Card 50 USD in a GVGMall.com shop once, but I would like to do the entire transaction through Steam, lazy as I am.
How to Gift money for Steam wallet?
Sign in to your son's account and add the funds if you don't want to buy a steam gift card from a local retailer.