What do u think?

When my sister was around 3 mom kissed her on her neck she said it made her coocoo tickle. We laughed it off thinking it was cute. She is now in 2ed grade and when I took her to the park last night the topic was brought back up. She told me not to tell he mother but she liked a boy (our mom would never let her have a bf) and that she told him to kiss her neck. She told me he did and she asked me if it would be weird if she asked him to kiss her down there. I told her not to and in my nicest tone I told her I would revisit the convo tomorrow after school (which is today). What should I say?????