It can be a problem if your child is unable to consolidate newly acquired skills through regular practice. Infrequent visits may cause your child to associate swimming with something that only happens when there is spare time here and there rather than as something to take seriously. Try your best to schedule at least once-a-week lessons. If you really cannot manage this, consider intensive learning sessions during school vacation breaks; many swimming schools, local councils and organizations such as the YMCA/YWCA carry out intensive courses that can teach children to learn swimming skills quickly but you have to commit to entire weekly blocks during this time.