Adult diaper pants and best diapers for baby girl have similar goals of absorbency but differ significantly in design and effectiveness due to the needs of their intended users:

Absorbency:

Baby diapers can hold much larger volumes given frequent wettings. Adult pants use absorbents optimized for smaller, less frequent leaks.

Fit:

Baby diapers form a custom contoured fit using tapes/velcro while adult pants rely on an elastic waist/legs which may not seal as precisely.

Leak protection:

Multiple layers, thorough sealing methods in baby diapers create a near watertight seal. Adult pants rarely achieve the same level of protection.

Size:

Babies come in standard sizes making it easy to find the right fit. Adults vary more in size/shape, so fit may not be as optimized in mass-produced adult pants.

Convenience:

Baby diapers are purpose-built for easy changes wherever. Adult pants require partial undressing, posing care challenges not issues with stationary infants.
So in summary, while both aim to absorb urine, baby diapers are explicitly designed with superior features to address the unique needs and challenges of baby care. Adult pants emphasize discretion over outright performance.