L2 flow

This morning as I walked into J's room, he was having trouble with his little tablet. He burst into tears and delivered himself of something very close to exactly the following:

Papa, ich wollte im Bett bleiben und ein bisschen mit diesem Gerät spielen, aber als ich es angeschaltet habe, hat es nicht funktioniert. Ich hab die Kiste hinten aufgemacht und es gab nur drei Batterien drin, und eine ist dann herausgekommen und auf den Boden gefallen!

This all just flowed out of him in one piece, obviously under conditions of emotional duress, and as far as I was able to tell, the grammar and syntax were perfect.  

I worry all the time that my son's ability express himself actively in German might fall behind his English. It seems inevitable, especially with kindergarten looming next year and the disappearance of our L2-heavy Mondays. I get stupidly paranoid every time I hear him falter in L2 or not find words (which of course kids—adults—HUMANS!—do all the time, even in their native language). So these moments of flow are very heartening.