I teach at a grammar school and quite frankly the best advice is let you children be. Don't push them, tutor them etc because if they have the 'ability' to pass 11+ then ok, but if you are tutoring your children, because without tutoring they would 'fail' (god forbid!), once they get to grammar (after barely scraping through the test) they struggle and lose confidence; they generally lack skills of creativity and problem solving and only know how to 'pass tests' yet are unable to truly actively learn.
It becomes all about the tests, the grades and obtaining approval; they learn from a young age that to 'pass' the test, to 'win' that place at grammar is a measure of their worth-these young people (human beings may I remind!) have so much to offer in so many different ways. Our world is changing, we will need all sorts of different skills, let's not let our children and young people down by stifling their innate ability to be creative, multi-skilled and adaptable. Remember they are your babies, would you really love them any less if they don't pass that test? That's exactly how your children see it!! Believe me I see the 'emotional fallout' at school!
The fact that you love them and are there taking an interest in their education and future is good enough.
Also if, like me, you have a child with AEN you really need to consider carefully the provisions in place at the school of your choice-some of the best AEN provision will be found at non-selectives and comprehensives.
Good luck!
Tired teacher.