I don't know how set you are on those particular trails, but I'd suggest some different ones given your situation (sounds like it's your first time there, and you have a baby):

Instead of Kalalau, do Sleeping Giant. (Though maybe not if it's been raining very recently, as parts of this trail can also be slick. Start from the east trailhead.) Also on the east side, Kuilau Ridge is an easy one with a nice view of the lush interior of the island and some tropical plants with amazingly huge leaves.

Instead of Kalepa Ridge, do one of the official maintained trails such as Awa'awapuhi or Canyon Trail to Waipo'o Falls. Walk down the trail a bit from Pu’u O Kila. Skip Polihale so you can spend more time in Waimea Canyon and Koke'e.

Since you're staying in Poipu, be sure to try Waikomo Shave Ice. That and Wailua Shave Ice in Kapa'a are the best shave ice on the island, IMO. And you gotta try Puka Dog once; not fancy, just fun--and definitely get the fresh-squeezed lemonade. (Ask for the lemonade with 1/2 or 1/4 sugar if you don't want it as sweet.)

And since you're spending all that money (or points) to stay at the Grand Hyatt, take advantage of the pools. I'm thinking the lazy river in particular would be nice with a baby.