That's shitty. Been there also. Bit epic but I've not written about it in 3 years and it will be cathartic so forgive me!
There were 4 of us. I moved away (though not so far and I always made an effort to go down at weekends etc) 3 out of the 4 of us had DC's.
For background- I used to send the other DC's a Xmas/Birthday card with a fiver in. My DC received nothing but I though "well, I don't give to receive etc"
One had her 40th birthday so, as usual, I sent a card. Heard nothing about a meal/party whatever. About a month after the birthday I arranged to visit for the evening at one of the houses. One of them was going to be absent as she had a newborn (of note also- I sent some flowers for her after the birth and sent a present for the baby)All was going ok, having a catch up when the 40yr old pulled out her phone and showed me some pictures of her, yup, birthday party. I kind of looked at them feeling awkward etc but said how nice the venue looked etc. To which she said "Oh it was great, you'd have loved it" Ummm WTF??
I was so flummoxed I froze, didn't say anything. Just sipped my wine quietly. After a while the conversation turned to outfits, what was so and so wearing etc. It dawned veeerrryyyy slowly on me that they were talking about an event that was happening the following Saturday. And it quickly became apparent that it was for the newborns christening
I asked if this was the case and they confirmed it. I mumbled about wanting to know the date so I could send a present etc but felt extremely embarrassed and upset. I left not long after.
I did send a christening card/present. After I'd got over the initial upset I thought "Well maybe I'm being precious/unreasonable. Perhaps it's a small affair, small church, family, close friends etc. The pictures were put on FB and it was held at.......St Pauls Cathedral. With about 400 guests. So I figured I didn't even make it into the top 200 kind of thing. It stung.
So (sorry it's long) it's been since 2014 and I've not sent one card for birthday/Xmas, nor interacted with them in any way via FB/Text or anything. I wanted to see if they would notice to be honest. I know I could have deleted/blocked them but I was curious. Nobody has said anything. And it's kind of gone on so long now (!) that I'll still not delete.
FWIW I have a very rounded life and lots of other friends, different circles in case anyone thinks I'm a bit stalkerish 
Not sure either if any of them are on MN, if so this is very outing! Wonder if any of them will be in touch......
OP I hope you do call them out as it's probably what I should have done 3 years ago 