What size clothing gifts do you like for your new born? (Crawling Age)?

My friend just had a baby and the gift I want to get her is little long johns with a sesame character and his name personalized on the bum. Now I sort of want him to wear them when he starts crawling because I think it would be cute. I'm not sure when they start and they sell these long johns for 6, 12, 18, and 24 months. Even if it had nothing to do with the crawling how high up do you like to get clothes assuming they will grow into them quite quickly?