If I'm not physically present with my wife, then I try to restrict my communication to texting. If I'm physically present with her (dropping-off kids or at an event for the kids) then I'll generally talk with her briefly and cordially. I usually wait for her to start the interaction, whether it's texting or verbal.
My sons, 11 and 13, are a little older than your children and they have their own cell phone. When I want to call or text them, I do that at my convenience. Because of the age of your children, yes, I'd just ask to speak to your children when you call. She may try to engage, and that's ok, but keep it short. It's not just important for detachment; anytime you talk to her there's potential for a bad interaction because emotions are raw.
