Ah in that case i will waffle a bit then! St Ives as you may know is a little fishing village - there are more like that in Cornwall and they are beautiful and quaint. Built before cars took over so driving round them is not advisable although you will be here out of season so it might not be too bad. My only worry with you not driving is if you want to visit the rest of Cornwall you may find a lot of attractions a struggle to get to. Im not saying its not possible for eg the Eden project you can get the train and take a park and ride, i suggest researching attractions beforehand to see if they offer this service from a specific town.
What do you like doing? There are a lot of coastal walks that are lovely and they are best undertaken without a car otherwise you will have to double back on yourself ha! If its attractions etc check out https://www.flambards.co.uk/
https://www.poldark-mine.co.uk/
https://www.edenproject.com/
https://www.carruan.co.uk/
There are lots of beautiful beaches around St Ives and hopefully you will be blessed with good weather to go paddling, grab a bucket and spade for the kids, go rockpooling and see what you can find, go crabbing (kits can be bought for a couple of pounds with bait to catch them in the harbour) depending on what is still running with it being the tail end of the season you could go on boat trips for pleasure or fishing! (yummy mackerel here).
Other things you should do are have fish and chips on the sea front (i will pre warn you, the sea gulls in St Ives will take food from you! Do not eat outside unless you are under shelter, they can be vicious. Unfortunately holiday makers think it is amusing to feed them and they have come to expect it and will do anything to get what you have, even ice cream!!! Most other places are not too bad just be careful especially with your children eating. Dont mean to scare you! Just wanted you to be aware so you can avoid the problem!!! Make sure to have a cornish pasty or two! My favourite is steak and stilton but the traditional ones are nice to. Try to find little independent bakeries instead of franchises if you can although most are nice really. Have a pint of real ale or three slurp...The sloop inn is quaint but be warned it is tiny!
There are animal sanctuaries like
https://www.screechowlsanctuary.co.uk/
https://www.sealsanctuary.co.uk/
https://www.newquayzoo.org.uk/
If you want to know anything else feel free to ask, told you i would waffle!
Finally for train info check out https://www.thetrainline.com/?href=ppcg_trainline&WT.srch=1&WT.mc_ev=click&gclid=CKbzgsWis7ICFYFlfAodr1gAYA
https://www.firstgroup.com/ukbus/devon_cornwall/
I hope all these links work, if not let me know. Enjoy your holiday
There is a train station there so you could get about to quite a few places by train, but make sure you check now far out of 'town' some of the stations are 
If you would like to see some lovely pictures of St Ives or get some ideas of places to visit, have a look at the 'Dreams Of Cornwall' Facebook page (see below for the link 
As for coastal walks, im not too sure about that area because its not the area i live in, but there will certainly be coastal paths linking up around st Ives. Oh and if your around gwithian and Godrevy lighthouse look out for seals, usually sunning themselves but to see them really clearly take a little pair of binoculars with you. 
