Any advice please!?!?!?!?!?!?!?

I'm sure they know you didn't mean it the way you said it and I'm guessing they aren't laughing at you per se, but at the implication they made up in their heads, which, under the circumstances, is not unusual. That will not likely be the last time you or anyone else makes an unintentional double entandre like that. People are fickle and find humor in the unintended. You are entitled to your feelings and can ask that your mom and sister not share that story, because it embarrasses you. However, your mom and dad have probably found many things you've done all your life, especially, things you've said as a toddler, that they found cute, funny and endearing. I believe this is just another one of those times. Hopefully, you can laugh at yourself on this one eventually too, so you won't feel so awkward.