Every child is unique and they all grow and develop very differently. JJ was taking steps by the time he was 10 months old and Miss E showed no interest in walking until she was nearer 18 months. now of course seven years later and you would have no idea as she is the far more agile and active. It all seems to even itself out in the end but getting there can be a challenge for some children.
There really does not seem to be any logic to how a child grows developmentally either, as like I said JJ walked at 10 months and was chatting away like he was at school at 2 years old but still he was not dry at night for quite some years. Day time potty training him all came easily and he was happy out of nappies in no time at all but cracking it at night is just that bit harder. There is no one reason for delayed bladder control at night but I believe it is inherited and until the child develops the trigger to wake them when their bladder is full they will continue to have accidents. Bed wetting is a perfectly normal part of growing up and affects almost 600,000 children in the UK every year, so no child needs to feel alone and it is always helpful if the parent shares with their child their own experiences.