It depends on your budget and on where you’re planning on staying. A short-term vacation rental listed in airbnb is a good option for families, especially if you plan to spend most of your days outside.
About hotels. In Marbella, for example, there is the Marbella Playa Hotel, which is very recommendable. It has pools with slides and a waterfall and an outdoor jacuzzi, as well as access to the beach. The buffet is very good, there are performances for kids at night, and a club for them to do activities and different sports during the day. Senator Marbella also has pools and good food, plus it has many restaurants and bars nearby. Aside from those options, you can choose one based on your budget and your preferred location.
For example, if you want someplace more affordable, you can try Hostal Enriqueta, or maybe Hotel Iberostar if you want to be close to Puerto Banús. In Málaga you can look into hotel Ibis or some smaller, simpler hotels like Casa Babylon or Casa Al Sur. Also, there are good family- friendly hotels in Mijas, like La Cala Resort, or Holiday Village in Benalmádena.
Hotels with water park
If you are traveling with children, you could look at booking yourself in a hotel with a water park. There are several in the Benalmádena/Mijas area, like Hotel los Patos, Holiday Beach Club and Hotel Holiday Polynesia, which all have water parks. Many of the hotels in Costa del Sol, especially in Marbella, while not having a water park per se, will have a couple of pools and some will have slides as well. For example, the Marbella Playa Hotel has a big pool with a slide and a small pool for children with a smaller slide (and an outdoor jacuzzi as well).
Costa Del Sol has many attractions for children, you can stay for a week and keep them easily occupied.