Most of the multilingual kids I knew growing up either spoke one language at home and another at school and/or had family that would speak predominantly one language to them (eg one parent would speak one language and the other another language, or parents would speak one language and other relatives a different language).
So your idea of making Tagalog the main language at home might be a good one ;D or you could have one of you speaking mostly English and one of you speaking mostly Tagalog and to pique their interest speak Tagalog while making it blatantly obvious that you don't want them to understand what you're talking about ;D
