Like your child's fingerprints on one large charm rather than 2 individual ones? This is perfect.

An extra large heart charm measuring 2.5cm by 2.5cm can accomodate 2 smaller fingerprints and short names(upto 4 letters) on the front or larger fingerprints with just an initial next to them.
Alternatively names can go on the back.

This charm can also be used for just one fingerprint if you require a larger charm.