Any mother will tell you that the best thing she ever did was have a baby. And, chances are, any mother with more than one child will also tell you that the best thing she ever did was have the second. The reasons for that, though, can be quite varied. Any mother will tell you it is magic watching siblings interact, and I could fill this page doing so. But I will say this: in watching my two girls together, I have at times been awed to witness acts of the purest tender love; at other times, been convinced that sibling rivalry is an inborn human quality. But there is another reason having two children has been useful and instructive. I am not a small woman, and I assumed my children would weigh in about my own birth weight (7lb 3oz). But both weighed in at just under 6lb. Although the second was a few ounces heavier at birth, she left the hospital a few ounces lighter because I refused to let the nurses give her supplements. (A word here to mothers-to-be who plan on breastfeeding: stand your ground!). They were skinny, no doubt about it. Their little legs were wrinkled and bowed, and they looked like little birds in big nappies. This was for a fleeting moment, though. What I noticed - and I would not have believed if I hadn't had my second child - was that although they both gained weight, they did so differently. Very differently, even though the variables were the same: nothing but breast milk for nourishment; nothing but snuggling, wailing, sleeping and pooing for activities. When my second girl was born, she grabbed my finger in the hospital bed and I had to prise it loose with all the fingers of my free hand. The doctor, too, couldn't quite believe her strength. The little round pads on her upper arms were not baby fat, but pure biceps. My eldest, now four, is the slender ballerina; my youngest, now two, is the big-bummed, rough and tumble one. I always think I will encourage the second girl to take up sports appropriate for her body type: weight-lifting and taekwondo, maybe. But like all little sisters, she idolises the older one, so she also loves to dance - and looks just as cute in a tutu. I have often heard it said that we are born with certain weight parameters, and that we are genetically predisposed to gain weight in certain places. God made us that way. I heard it, but that's not to say I wanted to believe it. I had always secretly held the hope that if I did enough time on the treadmill, I could prove this false. But seeing my two girls grow from birth has convinced me, without a doubt, that God indeed breaks the mould with every one of us. It is clear to me which of my girls is going to resemble their mother - and, after I finish my morning jog today, I'm going to have a croissant with my skimmed milk latte.