Welcome! You're definitely in for a great time here. I highly recommend familiarizing yourselves with the FAQs which explain things about how checklists work here, gaining permissions to do more, adding images (scans, no photos, please!) and trading.
And probably the #1 tip everyone who logs cards here should know: look for cards by searching for the player, click the "filters" link, and filter by card number. Doing that should eliminate a lot of your "I can't find this card" questions.
I hope you and your son have a fantastic experience on the site