Yes, a child can get impetigo more than once.  Speak to your GP if your child has had impetigo before and it keeps coming back.
Dr Friedmann advises, "practising good hygiene can really help prevent recurrent occurrences of impetigo - washing hands often and thoroughly and taking regular baths and showers. If you notice your child has a cut or scrape, or is irritated by a bite perhaps, or suffers with eczema, keep a particular eye on their skin and ensure those areas are kept clean and covered. Also keeping nails short and clean is always preferable."