I have a 3+ year old and am currently 31 weeks pregnant (due in July). I weaned my older son in November (at age 2.75) when the pregnancy made it just too painful to continue. My son really, really loved nursing, and I was surprised that he let go of it as easily as he did. He still holds "the nurses" when he needs comfort, and sometimes at bedtime, and that's fine.
As we get closer to the baby's arrival, my son has started talking about how he wants to start nursing again. Last night he told me that he wanted to "suck all the yummy milk out." I am a bit surprised by this, since it has been almost 6 months since he has actually nursed. Clearly the breast was very meaningful to him.
Various issues: I don't have any milk for him to drink and I am not interested in tandem nursing. We have talked a bit about how the milk (which isn't there now) will be for the baby, since the baby can't eat anything else. My son's response is to pretend to be a baby, with the theory that babies get milk and therefore he does too.
I'd love to hear how others have dealt with this. I don't want to take the breast away from him (even if he's not nursing from it) but I'd also like him to understand that he isn't going to start nursing once the baby gets here and I start lactating again.