I have experienced exactly this, but it was in combination with also switching from freelance to full-time employment. I used to have a new idea every day back when I was freelancing and didn't have kids. Now I'm lucky if I think of one every couple of months.
I actually think this is due to having less time to just explore the internet, read about interesting things, try out other products, etc. I spent a large amount of time doing that when I was freelancing and although it might seem like a waste of time on the surface, I believe it was what allowed me to connect certain dots about niche opportunities that weren't being exploited that I might not otherwise have noticed.
This jibes with my experience. You need a wide variety of inputs in order to connect the dots and come up with something unique. Time spent taking care of kids (for example) decreased my inputs, resulting in fewer outputs. Until I discovered audio books at least.
I actually think this is due to having less time to just explore the internet, read about interesting things, try out other products, etc. I spent a large amount of time doing that when I was freelancing and although it might seem like a waste of time on the surface, I believe it was what allowed me to connect certain dots about niche opportunities that weren't being exploited that I might not otherwise have noticed.