My sons are 15; their Dad and I get along great, but things STILL frequently get left at the wrong house and must be retrieved.
Reason should prevail:
* If it is not terribly inconvenient to retrieve something, do it. Remember that the kids did not ask for their parents to be divorced, nor to have to always know at which parent's house each of their possessions currently is and which possessions need to switch houses. It's great, if you were perfect about remembering these things when you were a kid, but not all kids do it well. Some adults always know where their car keys are. However, I - who do a pretty good job of keeping track of the possessions of 6 people - NEVER know where my own keys are. Luckily, I only live in one house, so there's only one place I have to search, to find them... Catch my drift?
* If it is a great inconvenience to everyone to retrieve something, don't. But be compassionate about it. This is a learning process for your step-kid. "I'm sorry that we don't have time to pick up your swim trunks. I know you're disappointed that you won't be able to swim. It takes time for everyone to get good at remembering to bring along all the things they need. You'll get better about it. And this isn't the last time we'll go swimming!" might be better than, "Tough luck! I always tell you to bring things and you never remember! This is what happens!"
* If your DH or his ex are willing to drive around and retrieve things, let them and stay out of it. If it starts to bother them, they'll be motivated to put more effort into helping your SS learn to keep track of his things...or at least to double-check, themselves, whether he has what he needs. But do you need to be irritated at them about it, if you're not the one shlepping around?
* If your DH IS asking YOU to drive back to his ex's house and pick up what SS forgot, depending on the situation/urgency, it's probably reasonable for you to say, "Look, based on my experience, growing up, I believe that kids can remember this stuff, if their parents let them suffer the natural consequences of forgetting. You see it differently. That's OK. You're SS's parent. You can handle it how you want and I won't give you a hard time. But put your money where your mouth is and drive over there and get his stuff yourself. If that's too much of a pain for you, then ask yourself whether my take on things is right - don't just dump the job on me."
* If you've promised a trip to the pool and SS doesn't have a suit, it's a real hardship on a kid, to be the only one not swimming. So that type of thing should be avoided, if at all possible. But let's say you guys bought him a PSP and let him take it to his Mom's, but he forgot to bring it back. What's the worst that can happen to him, if he doesn't get to play with his PSP until he returns to his Mom's? That sounds like a great opportunity to teach responsibility with some natural consequences. But again, you can be nice about it. Let him remember that he was disappointed with himself for forgetting his PSP (then he'll be more likely to remember it next time), rather than him mainly remembering that you got mad at him for leaving it at his Mom's.
* And where there's a simple solution...USE IT! Buy swim trunks for SS to use at your house (or on outings with you and DH), that never get sent to Mom's or Grandma's! Swim trunks can be as cheap as $5 at Wal-Mart or 50 cents at a garage sale/Goodwill. If the swim trunks he forgot the other day WERE the ones you bought him...buy him a new pair and start over, keeping them only at your house. If SS has other special clothes at your place, that you like him to wear to church, have him change out of them before his Mom picks him up! There are endless useful applications to the Keep-it-Simple philosophy.
Edited by VocalMinority - 6/5/11 at 2:33pm