Ah, this is actually a question about native fluent speakers vs near-native fluent speakers. The excellent English you hear in Germany is near native fluency. They get that by hard work and having a critical mass of English speakers. But the kids that hear the language at home as a family language, they get native fluency, and to them it will feel effortless. For the parent though, it will be work because they have to have discipline themselves to speak the chosen language and monitor if the kid is getting enough exposure to each language they need to learn.
Also another interesting point is that kids often speak the language they hear better than their parents-- this factoid comes from studies of non-deaf parents of deaf children who have to be models for sign language. The children speak better ASL than the parents, even though both parents have lousy ASL. So a child can get native-like fluency even if they have a non-native parent as a model. (I'm sure there is some bounds to this though- it's not magic)
I am a language hobbyist. I study languages for no reasons at all, so that's my bias. I want to say, of course! But someone already has posted that answer.
So I'll post the "no"-- don't do it if you got that nagging voice that says, "this is never going to work" If you already know you are low on motivation or have a shortage of resources, support from family, don't do it. At the low ends of success, there is just receptive fluency, usually because of too little exposure, etc. This is a bigger problem in the US where people just don't have a culture of language learning and have wildly unrealistic ideas about what it means to teach a child a language (like speaking English with a few token Spanish words)
I considered teaching my infant son French, but my French isn't good enough. Instead we're going for Russian, Tagalog and English.