This study examined the effects of variations in input on how children learn about cardinal number. A longitudinal study found that children who hear more number word utterances from their primary caregiver at 30 months of age say more number word utterances at that session and at 38 months of age. In addition, parents overall verbal input (tokens and types at the 30-month session) was positively associated with children's performance on tests of counting, cardinal word comprehension, and last-word responding at the 38-month session. The second study used the same dataset to examine the role that parents' gestures play in how children produce and comprehend cardinal number. It was found that parents who provide more gestures when talking about number have children who use more pointing gestures while counting. There was also a marginally significant trend for children of parents providing more gesture input during counting to outperform their peers on tests of counting and cardinality eight months after the initial observation. The third study was a training study examined how children exposed to different gestures performed on the Give-A-Number (GN) task and the What's On This Card (WOC) task, two tests of cardinality knowledge. Children who saw pointing gestures while counting showed significant gains on the GN task-compared with children who saw the same pointing gestures as well as a circling gesture when labeling set size. There were no significant effects of training on the WOC task. Gains on the GN task may be due to children recognizing that they needed to count in order to perform this task; pointing gestures during training may emphasize counting. In contrast, a circling gesture may distract from the object individuation that is necessary for proper counting, and may not help children understand that counting is the means to determining cardinal number. In conclusion, children's development of cardinality knowledge is related to spoken and gestured input they receive at home, and counting gestures, in particular, may confer benefits to cardinality knowledge.