I got 7 out of 10, because I wasn't familiar with the terminology, although some of it could easily be worked out. (We learnt about modal verbs, but that was possibly in French or Italian.)
It was fun, but I always did enjoy grammar* and am eternally thankful to our English teacher who had us analysing sentences and was very fussy about it. That knowledge (especially concerning the dative and accusative) has been invaluable for learning new languages, which I have continued to do all my life. It's not too early for kids of that age to learn about those concepts - the earlier the better, if you ask me.
While changes in the language and evolution are inevitable, a certain standard should still be maintained for spelling and grammar or one day we will be inundated by misunderstandings as no one will know what is meant.
*Also I was only an average pupil but excelled at tests and loved exam time.
How do you acknowledge Easter.