For the kids I'd bring their birth certs, certainly for the baby anyway. There is no requirement for this but when we brought our one year old to England last year I brought it just in case. To be honest I wasn't that comfortable with the fact that there was no way of knowing that he was ours, we could have been anyone. At least the 3 year old can tell someone that you're mammy and daddy. Anyway, no probs at dublin but when we were leaving the UK we were asked if we had his birth cert. Don't know what they could have done if we hadn't brought it, since legally there's no obligation to bring it, but I was glad we did.