Handling my parents and presents to my children

I just got a text from my wife, blasting my parents for mailing us a present for our youngest child (M 6mths), but nothing for our other son (M 3y). She's really upset that they have sent a present to just him and not the other one, It's not a Christmas present,.MY wife is furious, and I'm not happy either, but I don't know the best way of explainign this to them so they understnad it's a problem. I had similar problems when I was growing up, some years my older sister would get better presents than me and my brother, other years it would swap round, they never treated us all equally, and now it appears they're making the same mistake with their grand children.they get very defensive and I don't want it to explode into some huge argument where they end up saying "well if that's the thanks we get for buying things then we'll never buy anything!!!". We've had similar responses when we asked if they could make a change to something they were making for our wedding reception, it was basically their way or nothing. via /r/Parenting http://ift.tt/2GLxFY8