There are a lot of great affordable classes and activities to keep kids active in Graz!
Babies & younger children

Eltern Kind Zentrum (Petersgasse 44A, 8010) offers a wide range of classes and programs for parents and babies / small kids.

Kinderfreundehaus (Schlossergasse 4, 8010) offers classes, parent & kid groups (they welcome international parents) and even flexible childcare in the afternoon (3 yrs +) all at their cozy playroom at Tummelpatz in the city center.

Volkshochshule (Adult Education school) offers lots of affordable fun classes for parents and babies /kids (several in English too). They can book up quicky! If you or your partner work in Styria, you can also use your €60 bildungsscheck towards a class. Plus if you are on paid maternity leave, you may be eligible for €1,000 bonus to spend on certain classes. The VHS also offers a free supervised daycare room for babies and kids while you take a class (registration required). More info in my blog post here.

Mehrgenerationenhaus (MGH) Waltendorf (Schulgasse 22, 8010 ) is a small community center offering a baby group, kids classes and other fun activities.

Melanies Zwergerlschule lots of classes and also daycare
Sport Classes for all ages
The city of Graz offers sport classes for just €10! for school kids in the holidays (usually two hours a day for a week), also ski courses, ice skating and swim courses. Full day programs are also available for reasonable prices.

You can see the brochure with the overview for 2022 here. Places are limited and go fast. To be eligible you must have your main residence in Graz. If you want to sign up on-line, be sure to sign up for an account at partner.venuzle.at/sportamt-graz at least 4 days before registration opens so that it will be confirmed and active by the start of registration. Or you can register in person at the Sportamt (remember to bring your Graz residency documents for you and your children).
You can also find out all about kids activities in the holidays Steiermark wide on Kinderdrehscheibe’s on-line platform.
Adventure Centers

Wiki Adventure Park (Hilmteichstraße 110) offer an fun climbing course through the trees. Kids need be 110 cm for the easier courses (green or yellow) or 140 cm for the moderate / advanced (red, black). There is also a ground course for younger kids.

City Adventure and BLOC house both offer climbing courses and bouldering walls for kids and also parent/kids classes. Plus special areas for young kids.

Swim Schools
Delphinchen Schwimmschule for babies – 12 kids at pools around Graz
Playgrounds
There are 70 playgrounds around Graz plus several sport grounds (with table tennis, football and basket courts).
Other useful posts
Thermal spas and outdoor swimming pools
Libraries in Graz (great for boardgames, tonies and they have free program of kids events for all ages)
Drop off play centers (so you can get some peace and quiet for a few hours!)
Joanneum Museums, including the CoSA science museum offer fun kids activities. Kids up to 15 yrs go for free with the Zwei und Mehr pass (kids programs are an extra charge)
Gamlitz Motorikpark (45 mins from Graz)