Open them and play...admire the detailing, see if it peaks your curiosity to collect more...or just give it to your son. Most die cast, with a few rare as the exception, aren't worth a great deal. Not so much that it's worth the time saving one or two pieces like that in hopes of it having some future value. Some larger collections, and those rare ones, or chase vehicles in general have a bit more value.
It's like an old piggy bank I found my uncle had, and gave back to me a few years ago that was mine as a kid, possibly handed down from another uncle from his childhood. I looked up the value and discovered it might be worth $50 in perfect condition--which it's not. If i discovered it was worth a couple of grand I would probably be tempted to sell it. But I would rather keep the memories that go with it that sell it for a few dollars. And I suppose that's the most important thing in collecting anything. Buy what you enjoy in the here and now because so little of it will be worth very much. Collecting things for an investment might include coins, gold, original artwork...but toy cars, not so much. Unless you have a lot and are constantly selling and buying like a dealer, as some folks do.
