Can I have one?

On Shabbos, I lifted my shirt to ask AM (now 14 months) if he wanted to nurse. I usually nurse him in my bed privately in the mornings or before going to sleep, but my husband was davaning at hashkamah minyan so I was out of be supervising both AM and PJ (now 4). PJ saw me do this and asked, "Mommy, what's that brown thing under your shirt?" I replied it was a bra which is underwear for breasts for Mommies. PJ then asked if he could have one too. Not sure what to tell him I suggested he put on an undershirt because that's what boys wear instead. Luckily for me he agreed and went to his drawer to find an undershirt.