I advise you not to give up. It's never too late to learn a language (further).
I have two elementary aged kids who are German/English bilingual and have always lived in an English speaking country.
What has worked for us:
- I always speak to them in German -- I'm not the stay at home parent so every word counts
- Media in German (their favorite shows of their choosing -- it's too easy with Netflix and YouTube these days and they watch almost nothing in English)
- Playtime related to these shows' themes is usually in German because the kids assume the characters only speak German
- We participated in a bilingual German playgroup composed of around 10 families in a metro area of one million people -- larger areas no doubt have even better opportunities
- We believe any additional language is useful for opening up a child's mind and making foreign language learning easier in the future
My kids seem to have a good attitude towards being bilingual but maybe that will change as they age. I hope they will find it to be an invaluable gift when they are grown. It certainly is fun to share something special and unique with them.