Can't comment on Tregenna but we recently booked a wonderful cottage through Cornish Gems. I believe they do a range of holiday cottages and apartments and the site shows if the property is child friendly. We stayed in Bay Tree Cottage (put it into the search box) which was really well furnished inside and out. The prices are a little lower than some of the properties in St Ives itself but the location is ideal only minutes from the park and ride and with the beautiful Kidney beach a little walk from the house. Our little girl had a great time and we will are already looking to book for next summer