Lead in paint was banned from household paint from 1978 (16 Code of Federal Regulations 1303) in the US (other years for other countries).
For lead in plumbing - California enacted laws in January 2009 that increase public protection from exposure to lead in drinking water. The laws reduce the amount of lead allowed in plumbing components intended to convey or dispense water for human consumption.
However, EPA writes the following regarding lead in drinking water:
Lead is rarely found in source water, but enters tap water through
corrosion of plumbing materials. Homes built before 1986 are more
likely to have lead pipes, fixtures and solder. However, new homes are
also at risk: even legally “lead-free” plumbing may contain up to 8
percent lead. The most common problem is with brass or chrome-plated
brass faucets and fixtures which can leach significant amounts of lead
into the water, especially hot water.
Washing floors with water would therefor increase the chances of finding lead on the floor material despite it use lead free paint (if painted) and new plumbing system (that still can contain up to 8% lead).
Interesting too: The risk of lead poisoning in houses built before 1978 is large enough for EPA to require the following:
In January 2011 the US Environmental Protection Agency required that
all renovators working in homes built before 1978 and containing more
than six square-feet of lead paint be RRP-certified.
So in conclusion, based on probability, the risk of lead poisoning (running barefoot) is very low in houses of newer date ( >1986) (USA) but existing.
An absolute conclusion is impossible without actually physically measuring the materials and environment for the house in question.
To reduce the risk further, EPA provides the following tip:
HEALTH TIP: To help block the storage of lead in your child’s body,
serve your family meals that are low in fat and high in calcium and
iron, including dairy products and green vegetables.