working out the bra muscles

Reece loves to "workout" with his dumbbell weights and regularly asks if I want to go the YMCA to workout with him(he is 7).  I love that he does this but in order for me to leave the house it is a HUGE hassle to leave without the other two kiddos.  Usually when he asks me to workout with him I have a zillion other things going on and just can't make it happen.  It's a bummer but hopefully we can start a workout regimen together soon.  
So, the other day Reece was lifting his weight and he said "come on mom  workout with me."  He handed me a dumbell and I started lifting it (he had such a huge smile).  After a few minutes he said "man we are really working our chest muscles  or since you are a girl you are working your bra muscles."   So funny!