I think grammar or not, supporting your child from Reception onwards is never wrong.
We read to DD since she is a newborn, we normally read a level higher than she can read herself. For example we currently read Famous Five and similar while she reads Rainbow Fairies (thank you school) or similar levels.
We normally hit the library so she can choose books for her and we then get a chapter book for bedtime story. She has lots of books on her own, I normally hunt them down in charity shops or at The BookPeople so the odd mistake is not too costly. We never followed any reading scheme, that's the school's job, mine is the fun reading.
We also do lots of board games, Scrabble, Monopoly, ludo, snakes and ladders, all kind of Orchard Games. Jigsaws, puzzle books for problem solving.
You can introduce maths in everyday life, baking, shopping and reading the time.
Topics like history, science and geography leads to further practise in reading, writing and maths.
If around Year 3-4 your child emerges as a candidate for the 11+ you will need to prepare for the exam formally. Kent tries to make the exam un-tutorable but you would still be able to find out what the exam contains and make sure your child is knowledgeable.