When my dad visited earlier this month, we took the opportunity to go try out the local amusement park - Divo Ostrov. Located on Krestovsky Ostrov (ostrov = island) it is a mix between a local fair and Disney. We went during the week, which partly explained the absence of people; the oppressive heat may have also played a part - smarter folks were probably flocking to the water park.
You can either pay per ride or get a day's pass. We opted for the pay-per-ride but will give it a good think next time. There were plenty of rides Alex was big enough to go on, and some required adult accompaniment and some didn't; some charged for the adult accompaniment and some didn't. There was also a decent couple of sets of playground equipment, one for the preschooler and one for older kids - free of charge. In addition to the kiddie rides, there were plenty of adult ones with roller coaster and bungee jumping things I would never set foot on, as well as an arcade, a roller-skate rental, a Segue rental, plenty of tchotchkes to buy, some fair-type games, and several cafes. Given my bulk of experience in the USA with these types of parks, I was amazed at the tastiness and the reasonable prices at the cafe. I shouldn't have been, of course, as Spb is one of the better food cities I have lived in (or, for that matter, visited).
No funnel cake though :(