Hi,if you like sidari then you'll also like Tsilivi in Zakynthos(Zante),there's loads of family friendly bars with entertainment going on,or quiet cocktail bars if you prefer that,stacks of restaurants and all pretty cheap yet good quality,for the daytimes there's a massive mini-golf place wioth 3 different courses,a small water park in resort or the main larger one a bus ride away,plenty going on down on the 3 or 4 different beaches,loads of shops etc for all the usual stuff and coming from someone who's lived and worked in Greece for many years i'd say it's the friendliest resort i've been to(i dont live on zante by the way so not biased in that respect).

Apartment wise the Planet looks pretty good,got to know the staff in the bar there(best bar in town)and had a look round their pool etc for future reference,also the planos bay looked good and this has the waterpark on site. only hill we found in the whole resort was literally a slight incline up the main road from popeyes restaurant but this was so gradual and short that it barely warrants a mention.

Avoid the Zante maris though,see my review from this september!

Alternatively try Pefkos on Rhodes,not as big as tsilivi but still a nice place and family friendly(i AM biased towards rhodes hence i try not to go on about it on here,only fair).