Aspiring artists have reached for paper and pencil for centuries, but papers vary. Those that contain acids will discolour and turn brittle. Paper living in a damp place is a party location for them. Pencil is a very stable drawing medium. The pigments that give colour to charcoal and chalks are stable in light, but the unfortunately can be easily smudged.
Pastels powder as easily as chalk, but some colours are susceptible to fading.
Although artists have experimented with fixatives over the years, collectors should refrain from using them. Modern fixatives may change the colour of some pigments and can seal in dirt. Put these drawings behind glass - the particles are light enough to be lifted by static electricity if framed using acrylic. Hang them on a wall free from vibration - a slamming door or rattling furnace can shake those fine lines free. In many cultures, over many centuries, lines have been drawn in enduring, carbon-based inks.