In our current understanding of particle physics, elementary particles such as quarks and leptons are considered to be point-like particles with no known internal structure. The fractional electric charge of certain elementary particles, like quarks, is a fundamental property of these particles, but it doesn't imply a division of the charge itself.
Quarks are believed to be the fundamental constituents of protons and neutrons, which are composite particles known as hadrons. Quarks come in six different flavors: up, down, charm, strange, top, and bottom. Each quark flavor carries a specific fractional electric charge. The up quark has a charge of +2/3, while the down quark has a charge of -1/3.
The observed charges of composite particles, such as protons and electrons, are always integer multiples of the elementary charge carried by an electron (-1) or the proton (+1). The fractional charges of quarks are only observed in the context of composite particles and are not directly observed as isolated particles.
Quarks are confined within hadrons due to a property known as color confinement, which means they cannot exist freely as isolated particles. This confinement prevents the observation of fractional charges in isolation and is why we only observe integer charges in everyday matter.