Just wanting to chime in w/ a more neutral experience... my kids weren't too sure about the clubs the first time around (ages 5 and 8). They liked it ok, but didn't really want to stay more than 30-45 mins at a time and not really more than once a day. I honestly think a lot depends on the kid's personality AND also whether they're used to being left places w/out you (like other childcare, for example).
Anyway, the second time around (ages 8 and 11), our were willing to spend more time in the clubs and even started asking to go there. Not like 24/7 but noticeably more than the first time. I don't know why... maturity, being more comfortable in situations w/out us, being used to the place (same ship as before), better connections w/ the kids there, who knows. My point being that it can VARY A LOT. So just be prepared... you might try the first time asking them to stay in the clubs and hour and then go do something onboard where you won't be annoyed if you need to come get them early.
Also, here's another thought: you said you have older kids. I *think* you can set the permissions allowing them check-out your younger ones. Then you could ask the older ones to be "on call" when you're at Palo or whatever.
Lastly, we also did what others have mentioned here, which put the Cruise App on their iPhones. They wouldn't have the first clue about how to text on the Wave Phone, but they quickly figured out how to text via the App. This made it super easy for us all to touch base and was esp. awesome when the answer was, "No mom, don't come now- can I stay longer?". As an aside, the CMs will call you on the Wave Phone (not the App- so make sure you're bringing a Wave Phone when you leave them in the clubs) if your kids ask them to (unless you've told them not to bother cause you're off the ship or whatever). That being said, we preferred the simplicity of the kids being able to to text us directly.
Hope that helps!