I would say 6, it has structure and transitions as expected in IELTS, however I find few places (marked in red) which don't seem to be right to me. If they were not there, 7 should have been fine.
1. You need to be careful with your spelling, you may use them correctly regularly but your IELTS evaluator doesn't knows that. Children is a very common word, writing it incorrectly so many times would raise eyebrows for any evaluator.
2. You don't have to do ostentatious display of vocabulary but try to use some non-vernacular words, there is a subtle difference between the two, you need to do some practice for that.
3. Dont keep using word childrens, use synonyms like youngsters, kids etc to avoid repetition.
4. I would say 'always has an' sounds better than 'has always an' as highlighted in red.
5. play on themselves ? I would say play by themselves
6. You used 'a' and 'an' quite sparingly.
I am no english teacher or native english speaker, it would be better if someone else can chip in.