My youngest brother is 17yrs younger than me (half brother) and he was just over two when I moved out of home. Until that point we were quite close as I would do a lot for him when Mum was busy with the other kids (I have two brothers and a sister also younger than me - same parents) plus a step brother. Plus i would be the babysitter if Mum and her partner went out etc. Even after I moved out of home my little brother would come and have weekends with me and I would take him places and stuff. Now that I have kids it is more a motherly role I have with him I suppose, but still sisterly kwim? My kids just adore having him as their Uncle though and he was in his last year of primary school when Lindsay started school last year and he thought it was so cool to have an Uncle at school with him.

Like Lulu said, it's what you make of it. No doubt you will be seeing a lot of one another and the three kids will grow up together so there's no way you can avoid having a bond with them.