As their origin is in Canada, I guess they have Canadian passport so no need birth cert?
If HK citizens no need birth cert to travel but, if touch wood need to see doctor during the trip, you might need birth cert to prove you are bb's parent as it is only document could prove.
希望勉勵一些有任何困難的人,要勇敢一些,有能力幫人就去幫,不開心時不要怪這怪那,上班時不要推卸責任! From myself, 兔唇mama
鏗鏗MUM: 人窮,慾望琳瑯,不爽不吃;志不窮,路途瞭闊,不吐不快 : )