Another good way to keep kids e-safe is to keep the computer in a family area - so 'no secrets' - and to agree what should be done if child sees something that is unpleasant or experiences attempted grooming ie someone makes them feel uncomfortable. I'd recommend you keep the blame out so child feels safe in going to you or another adult to 'tell'.
Kids can see nasty things in a newsagents or on telly - the internet isn't unique in that respect - so you can't expect to be able to prevent a child ever encountering 'stuff' online, but what you can do is work out together how you will deal with it.
You can download a little gizmo called 'Hector protector' which is intended for quite young children, and puts a dolphin avatar on the browser that 'protects' the viewer till an adult comes and resolves the problem.
Your son's school should have advice for you as well, as part of their e-safety policy, but if they don't you can get e-safety info from Kent Grid for Learning.
Ultimately no single piece of software can automatically prevent children from deliberately or accidentally accessing inappropriate sites. It may appal you to know but some of these sites deliberately evade filters and are passed between adolescents as 'the currency of cool'.
However, automatic filtering software can block important information sites - I came across one software that blocked all references to Jane Austen because one of her books has reference to a Victorian ladies handwarmer, or muff....
OOps that's me probably blocked for ever by AB for 'using language...