Sorry for the late reply.
If you don't practice a language very frequently, you can forget easily, it's the same with me and english, so I try to speak (write?) as much as I can, and this kind of forum is a good training^^
German is a nice language too! I hope that your son will learn a lot ^_^
And thank for the welcoming! I'm very glad to be here =3 The forum seems very nice.