We currently put £10 per child per month (which is what we can afford at the moment) into savings for them, in their joint names with me. They are special accounts for children's savings. Their birthday / Christmas money from aunts and uncles goes into the same account.
The CTF are separate, and we don't add to them.
The plan is that when they are 18, they can have their CTF money. However, I know what I was like at 18, and so the rest of their savings are protected from a massive spending spree! 
When they are 14, they are able to withdraw funds from their savings when countersigned by me, but until they are 18 they can't make independent withdrawals. If DH & I feel that we need to, we can move their savings to a different account, and not tell them where, as they approach their 18th birthdays. If needs be, it will be locked up in trust until a later date.
I know on here that can be controversial, as I've seen MNers posting before that it's "their money and they should be able to do whatever they want with it". BUT I also know that the great aunts and uncles who have contributed over the years would not want it pissed up against a wall - it was given to them "for their savings account" with the intention that they could use it for something they need in the future.
They are 6 and 3 at the moment.