We stayed at this beach-front apartment in Sitges for a week in June 2016. The apartment was the perfect size for the three of us (myself, my partner and our 4-year old), and was also reasonably priced compared to other apartment rentals we'd considered in Sitges.
The best thing about the apartment is, as it says in the description, it's beachfront and only 10 metres from the marina beach. It's also part of an apartment complex which has a pool, a toddler pool and a poolside bar/cafe under an awning (the cafe's open in the summer season only apparently) so you have the choice of beach or pool.
The owner was really responsive both before and during our stay if we wanted to clarify anything or needed anything.
The apartment's a bit out of Sitges - at least 15 minutes walking for an adult (or 30 minutes plus with a little one in tow) which turned out to be a bit ambitious for us in the heat - so bear that in mind if you've got small children. That said, the local bus runs every half-hour from a stop near the marina, less than 5 minutes walk from the apartment - so you can ride the bus into town in 15 minutes.
We liked the two beaches between the marina and the town - Platja des Balmains is mainly nudist, but it doesn't matter if you want to keep your swimming stuff on!!
In terms of food, we ate out in the the marina most nights, as it's only 5 minutes walk from the property, and would recommend Villa Marina for being child-friendly and good Italian food, and also the Pizzeria del Puerto. We'd also recommend La Caleta, the bar/restaurant just above the Platja des Balmains, for their excellent brunch for only 6 Euros each and fantastic sea views. The local Carrefour supermarket is about 10 minutes walk from the apartment so it's easy to stock up on provisions too.