Our children do light up our lives, anyone knows that. Without them it must be do very hard. Be kind to people, it hasn't happened to you but surely you've empathy for those that have.
This is how you feel, Allsorts, and it is fine. But it does not suit everyone. I find the phrase about children, or anyone, "lighting up" my life distasteful, by which I mean such a phrase is not to my taste.
I would not use it, I understand both that it appeals to some people and that it irritates others, as the OP intimated.
It is not unkind to say all this.
Losing a child has happened to me. Much as I love all my children, I would never say they lit up my life. That phrase feels totally inadequate to me.
If other people want to use it, that's fine. If other people think it's too sugary (or whatever), that's also fine. How about everyone just being accepting of differences without accusing people who disagree with them of unkindness?
And it's still okay for someone to have a grump. People having grumps happens a lot on Gransnet, especially about the words and expressions people use.