All in all, it depends on how much work you want to put into the account. With the kids being 6 and 4, the time horizon is very long. Obviously, when your child is 16 years old and may need the money in a couple of years, this changes the overall asset allocation of the account (or at least it should). You don't want to have a 100% equity account when your child is 16 years old, as you run the risk of them needing to draw down on the account during a bear market or stock market crash.
But with 12 and 14 year horizons (and that's assuming they went to college/university immediately after graduating) you've got a lot of time to withstand the peaks and troughs of the stock market.
I guess you have to ask yourself what type of work you want to put into the account. If you're happy to monitor it all the time, rebalance it, make changes etc, then a portfolio full of stocks may suit you. But if you just want to contribute, set and forget, you could potentially look at an all-in-one ETF? Something like VEQT maybe? These funds are becoming very popular, especially for those who just want to buy and forget about it.
When time horizons are long, becomes more of an individual risk decision. But when time is tighter as I mentioned above, it then becomes more of an asset allocation decision.