The biggest mistake we made was putting all our reserve funds into ETF's. We got a little carried away with the idea that all available money must be working money and when there were times that we had to pay off a big bill for vehicle repairs, it was a hassle to sell funds and move it around. This year I plan to keep our reserve account separate so it's available when needed.
We've set up money market accounts for our kids since they were born and they were earning pennies each year. We put all their money into separate accounts in Vanguard and invested each into ETF's. It was really fun to watch their money grow throughout the year and I've been working with the two oldest to teach them investing basics. If they can learn at a young age they could be set for life. This year I want to put money into each account for their birthdays in addition to whatever presents they get. I think that could be a good tradition.