Probably by then the best options would be Rhodes , Kos or Crete (Chania end is nicer in my opinion) as they will certainly be the warmest . Look for islands on the east of the mainland as those on the west are notoriously wet by then (that said nothing ever seems to be standard year in year out especially with 'global warming')
We have booked with Manos (website: http://www.manos.co.uk/AniteNextPage.asp?p=HOME&s=82900181 ) for our hols in September and there seem to be a few bargains , and also several are daytime flights which you will probably prefer with a child. You're looking at around £220 per person (adult fare) they also seemed quite organised we have had our tickets for ages and they have been really helpful on the phone.
I shall reserve judgement until we have been though & report back.
greeklass x

Hi Karen. We have been to Crete and Lesvos in October and had good weather both times. We stayed at Chania in Crete and Petra in Lesvos. Crete did seem to be busier at that time of year than Lesvos if I recall but both places are really nice but if I had to choose I would go for Lesvos which is still very Greek! (Dont get me wrong, Chania is not commercialised - at least it wasnt when we were there about 9 years ago). Petra is close to Molyvos which is gorgeous; full of cobbled streets, with a castle and nice bars/restaurants near the waterfront. Gail

Yes Lesvos is really nice & unspoiled however it IS a long trip from the airport - at least 2 hours to the resorts - probably not wise with a 5yr old.

We went to Crete once in october last two weeks of the holiday season we had temps in the 80`s

we were in Crete last October stifling during the day but cooled off somewhat in the evening's

wizard

We travelled to Lesvos with a 2.1/2 year old

I think October is very iffy for weather in Greece usually, but do think Rhodes, Crete, and yes Lesvos would be best, all depending on what you want remember Crete is Cretian first and Greek second even their music reflects this
pojo

went to crete early october last year and stopped in hersonisos.stopped in marni village really nice(they even sent us a christmas card). travelled around that side of island, would stop in stalis if i went again due to the closeness and quality of beaches.the weather was really lovely that time of year ,not as hot as cyprus the year before.we are off to rhodes town this year,again early october

Hi Karen, went to Santorini last October and Rhodes the year before in October.....it rained on the way to Rhodes so the first few hours were a bit bad but then cleared up all week fine and sunny. Santorini no probs at all, rained for 1 hour 1 night, that was it, it was the first rain they'd had for about 4 months!!! We're also going to Kos this October...from past experience any of these islands and Crete you should be ok for the weather...

Don't go to Corfu at the end of Oct, which is usually when the kids holidays are. As most of Corfu is shut. Well that is what we found when we went.

Yes October and Corfu don't really mix friends went several years ago to Corfy Mid Ocober and had two weeks of rain and several taverna's closed we have been to Kefalonia in October had it realy hot and also very rainy it's the chance you take.
pojo