We are flying out in 2 days with our children (8 and 12), and they love the Oasis. One tip - it goes really cheap after 3pm (or is it 4pm), rather than paying the full day price you only have to pay a couple of euros which is good if you just want an hour there.
The Lido is also quite good as well, has a nice cheap bar. For years we didn't go in even for a look as we assumed with the guy on the gate and a till you had to pay, but we discovered you only pay to use the pool so can go in and have a drink and a look around for free.
You can see the lido on the live webcam bottom left...https://www.skylinewebcams.com/en/webcam/espana/canarias/santa-cruz-de-tenerife/los-gigantes.html
My pool is bottom right so please ignore the large pale fat bloke you may see splashing around.