Well, if by 'make the most of it' you mean give it the chance to grow as much as possible, you probably want to look at investing in the stockmarket. You'll need to understand that the value can go down as well as up, but research from Barclays Capital shows that over any 18-year period you care to look at going back to the year dot (I'm paraphrasing, but it was at least the 1960s) an investment in shares has finished higher in real (ie after inflation) terms than when it started. (As a caveat, I have a small investment I made right at the height of the silliness in 2000, when I was very poorly advised by an IFA - the £1000 I put in is now worth £700-ish - but that's pretty rare.)
There are plenty of children's savings plans available from the likes of F&C, Baillie Gifford, Witan and (I think) Henderson - they all invest in investment trusts, which are funds that in turn inevst in shares, often from all over the world.
You can usually opt to hold these either through a 'designated plan' or a 'bare trust'. A designated plan remains your property, so it is ultimately up to you at what age you give the proceeds to your children. A bare trust has tax benefits (mainly for inheritance tax) but becomes the property of the child at age 18. There used to be trusts where you could specify the finishing age, but there was a big shake-up a couple of years ago as a result of which they became so unattractive that they essentially ceased to exist.
If your children are under 8 you could use their Child Trust Funds, though these only allow you to invest £1,200 a year (that's £300 a month with three though, so you might feel like that's enough!)
The Government are currently working on a 'Junior ISA' to succeed the CTF - it may well be that CTFs will roll over into these new accounts. They may have a higher annual investment limit, though there will still be a cap. They haven't finalised the details yet but the new account is expected to be introduced by autumn of 2011.
As to finding an IFA, try www.unbiased.co.uk which can give you the names of IFAs in your area. It won't tell you how good they are - I guess the best way to gauge that would be to Google their names and see if any horror stories come up!
Good luck - and sorry for the rather long post.