Ideas about numbers and counting form early in infancy: well before the need to see printed characters on cards.
Touch, sight, and speech are the main inputs. Try to direct some of your everyday conversations to numerical matters. Try to make some special time to discuss counting stuff. The printed cards may occasionally be useful for graphical illustration: bring-in a card or two as opportunity arises.
History suggests that people who had few – or no – things had no need to count. Nowaday's your child's world is aware of the plurality 'things' long before the need to talk, write, or communicate about them. That awareness needs to be enriched: at home, as well as at the more formal group activities. The cards themselves are not suitable 'things' for your child to count.
The printing on a card is a visual code for one specific counting digit. Gently introduce lots of other countable things at home: you are providing experience. This awareness will mature into numeracy in time: perhaps from age two or three. Children love learning to count – especially if it is meaningful.
In life it is important to be clear, when communicating, as to what 'things' are under discussion. Especially is this so in arithmetic. Mathematics falls apart if there is confusion over 'things'. The words, symbols, and codes for counting 'things' must be clearly understood by both parties in any communication. I have set aside another page to expand on suitable 'things' to use at home.
Some adults may well not be tuned-in to their child's understanding of adult language. Speak slowly, clearly, with simple precision, grammatical accuracy and without steretcing the child's vocabulary. Your child may not experience such care when in outside-home company. It is important to clear up misunderstandings as the occur: it only takes a daily few minutes.
This topic is at the bottom of the page for good reason. In our sales literature, and elsewehere, we have been most careful to avoid linking the two. The cards are just one of the small aids that will help you to communicate with your child when the time is ripe. They are not offered for sale under the banner of "These cards will teach your child to count". Your child will learn to count of his/her own accord, and will be all the better for it in later years with your time and help. The cards are intended to illustrate conversations and understanding about 'numbers'. Adults know it all: children are just starting.