For me, taking the day tours from Torre would be better with a 4 year old in tow and at least you won't have to do the driving and can relax and take in the view. A day trip to Malaga, however, is really easy from Torremolinos, just get the train, cheap, clean, regular and quick and your 4 year old will probably enjoy the experience.
A day trip to Granada from Torremolinos is easily arranged and will guarantee you a ticket into the Alhambra, not as cheap as going by public transport but worth it. Ronda, is a wonderful day out, you can get day trips or, you could get the train to Malaga and then the train up to Ronda. You can take a day trip to Mijas Pueblo - they have donkey taxis there which you little one would love. Also, as a break from travelling, take a trip to Fuengirola and visit the Bioparc. Its a wonderful place with lots of animlas and birds to see and although some see it as a zoo, it actually is a leading conservation bioparc, small but feels like its a huge place. You could also go to Paloma Park in Benalmadena which has rabbits and guinea pigs running free, with lots of chickens and peacocks and other birds too.
My advice would be to do:
Malaga
Granada
Ronda
Mijas
with side trips to Fuengirola, Benalmadena for some things for your 4 year old.
Hope this helps.