I really wouldn't recommend November. If the trip has to be in November I'd go somewhere else to be honest. November is, on average, a horrible, grey, stormy, gloomy month. Usually too early to snow but also low daylight and high chance of strong winds and rain. I'd also probably wait until they are at least a few years older, really.
I have a 6 year old and a 4 year old and there are lots of fun things to do, but most of the things that make Iceland special are not great for that sort of age range. The main exception would be the swimming pools, which are excellent. If you like slides, Lágafellslaug in Mosfellsbær is one of the best. Otherwise the kind of things you can do with children are the same kind of things you could do in many other countries, so not worth the expense of coming to Iceland.
When they are a bit older they are more likely to be able to enjoy glacier trips, mountains, waterfalls, rafting, super jeeps, horse riding, etc. Many activities and areas are only accessible in the summer and the weather is also a lot better then, so I would always say to come in the summer unless you particularly want to see the northern lights in which case September/October is better.