Is there any particular reason why you are looking at investment bonds? The Standard Life Capital Investment Bond, for example, takes 4½ pages to explain the charges and then they want more if you want to cash in your investment within 5 years. As bonds pay tax on your behalf rather than you paying after a tax return, the bonds can sometimes mean that more tax is paid than necessary and this cannot be reclaimed (as your grandchild may not pay tax, this should be a major consideration).
You should compare the bonds that you are considering with some of the larger unit trusts and investment trusts. With these, the charges are easy to understand, you can track your investment easily and, when you want to cash in your investment, you just make a phone call and a cheque comes through your letterbox with no "penalty" charges deducted. If it's your investment, should you really be paying penalties to get your money back? With all larger unit trusts and investment trusts you can invest lump sums (the minimum is often £500) and monthly payments (minimum often is £50). Many also offer plans specifically taylored to investing for children (F&C's children's investment plan, for example, has lower investment minimums at £25 per month or £250 lump sum).
Whatever you decide, you should not put all your money into the same product.