All children develop at different schedules, which is why a parent shouldn't necessarily be alarmed if their child isn't yet pronouncing words as properly as others in their age group, or according to a parent's expectations. Some children will also simply outgrow a lisp or learn to enunciate as they get older; remember that a child's mouth, tongue, and muscles in the jaw are still developing when they're very young, so they may learn to pronounce difficult words and sounds as they become more physically capable.