I know, an old chestnut but I am not sure laburnum is a suitable wood for a baby item. A rattle is very likely to end up being sucked and possibly chewed and the wood is classified as toxic. The wood database says 'constitutional effects (nausea, vomiting, headaches); direct toxin' Whatever finish you use on it will soon wear of in the hands of a baby and there's no guarantee that the child has no allergy to the wood. Please think again anout this.
Pete