I'm in the same situation as you nantucket66. Have 400D from years ago, I havent had much time for photography over the past 2 years but now have a young family and would love to capture moments with good quality photos.
I was toying to get 5diii but recently read about Olympus OMD EM1 with their new 12-40 2.8 lens. You should have a read about it might suit your needs.
Just use your 400D it will still take great pictures! then if you get into it or find yourself limited you can upgrade as required you certainly don't need a new camera to capture quality photos!