DS is now 15 months and has been crawling since about 8 months. He's just starting to take a couple of first steps too 
His crawl has always been lopsided. He doesn't drag one leg, but instead uses his left knee and his right foot. He's always done that and I haven't been worried because I thought it was common.
He can kick really well with both legs and gave me a good kick in the stomach this morning whilst changing his nappy.
However, now DP has a bee in his bonnet because the nanny said that DS only kicks with one leg whilst swimming and that it might be a hip problem.
I honestly don't think there is anything wrong with his hips - it was checked at birth and then at the 6 week check by the doctor and they found nothing wrong. He kicks evenly.
Is this all normal, are we worrying over nothing?