Every time you wash the children's clothes - you harm the world in which they will live. Fabrics shed masses of microscopic plastic threads, or microfibers, when washed.
Most of these particles pass through the filters of sewage treatment plants and end up in water bodies and oceans, where animals absorb them. The dryer vents also emit particles that are carried in the air for long distances. It is advisable to try to reduce the 'washing pollution' until less polluting fabrics are invented.