Jealousy sometimes means we're not feeling worthwhile, meaning worth loving, worth coming first, worth being considered...
Two important things to keep in mind:
1) Your instincts may be telling you that there's more to this relationship, or it may be your fears that there's still romantic love (and therefore a threat?). Be careful to separate your gut instinct from your fear. This is hard work. Sometimes a good (and I mean good) therapist can help. It can also get you on the road to truly believing that you are valuable, and your worth doesn't come from how others treat you, and;
2) Be careful not to create the very thing you fear. Showing signs of jealousy (when in fact there is no basis for the worry) can push the other person into moving away from you.
However, above all, know that just being a good, trusting, caring and hard-working person will reap its own rewards, over and over again, throughout one's lifetime.
You seem to be cognizant of the fact that the positive communication between the exes benefits the kids. This may simply be an indication that the two are determined to create a low conflict, upbeat scenario so that kids can learn from their role modeling. This is a great, great, great thing. Very admirable. If your heart of hearts says it's in your head and there is no real threat, then move forward with your head held high.
However, if you can't get past this thing, I agree that finding a way to tell your wife that you have feelings you can't suppress, share them and see if there's some reassurance you can get. But be careful how you present it; let her know you trust her and understand that she is a good person and mom.