This whole FOMO thing isn't as real, nor as detrimental, for kids as people try and paint it. That's not to say there's not an impact, but kids survive just fine - everyone misses out on this and that, even adults who opt out. Nobody ever keeps up or is involved with everything everyone's doing. Learning that that's okay, and how to handle that, at a younger age pays dividends as an adult.
Besides, there are many ways to still keep your kids connected to their friends without feeding the beast.
And I say this as a parent.