The way disposable diapers work to absorb pee is through the use of SAP or Super Absorbent Polymer.
The diaper soaks up pee because of the Super Absorbent Polymer that swells up as it absorbs the liquid.
This is why when a baby or toddler pees in a diaper the diaper swells up and gets squishy because of the SAP.
SAP in the diapers can soak up and hold the pee away from the skin which is what makes disposable diapers much better than cloth diapers.
With Cloth Diapers they just soak in the urine but a child wearing cloth diapers feels wet and is more prone to diaper rashes.
The disposable diaper does not really feel wet against the child's skin unless it's at the point of leaking.
A diaper should be changed before it gets soaked enough to leak but sometimes it happens.