My 3+ yr old is not in kindy either at the moment due to moving, no places in community care and then the prospect of moving again and not wanting to muck him around too much. He is the age for school next year though so I am keen to get him in somewhere now we have moved and settled so he can become reaccustomed to some of the routines like things more like school and also to make some other little friends since we are new to a small town and know nobody.
Given he is the second child I don't think he's missed out on too much (including mental stimulation) over the last 9 months though cause he's always involved if his brother is doing homework etc. Wants to read, count learn etc. in reality there is not too much except writing - he won't do that for me cause he doesn't want to be wrong - that he doesn't know, so academically he is ready for school next year but I think at least 6 months of a couple of days for the rest of the year will help him socially fit in better next year and know a few children before he starts with "big" school.
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