It's also been great for Jon and I. We have time to talk while I cook dinner. We can actually have a conversation about our day without interuption.
I started this "outside until dinner" time early in the Spring so they could get used to it as summer approached. When we have a hot day, I send them out with buckets of water and rags to wash their ride-on cars. This summer I plan to fill the wading pools most days to give them a chance to splash around when they get hot. Of course, in the summer they'll be outside earlier in the morning and later in the evening to avoid the hotest part of the day.
I think it's about time kids spent more time outside and less time playing battery-powered toys that do the thinking for them. Fresh air, sunshine, and time without parent-directed activities.... important parts of childhood, if you ask me.