To envy my sister's freedom?

It’s certainly reasonable to feel the way you do, I envy my friends without children who are able to be spontaneous and get away. What is unreasonable, not saying you are doing this either, would be to treat them differently or act out on them because of the way you feel. You can acknowledge how you feel, while also realizing they are not doing anything wrong and therefore should be able to come to terms with it within yourself to not let it come out sideways in your relationship. Resentment over things like that can be sneaky though and can hide, so do take care to digest your feelings towards it and address it internally so it doesn’t show up later between you two!

My sister went on a break a way to a location I've wanted to go for a long time, due to my children having no interest in this, I know i won't be following in her foot steps anytime soon. Not dragging 3 kids somewhere they will be bored.
Yeah I felt a pang of envy when she told me, as I know it will be a few years till I can do it for myself. She had an amazing time and did nothing related to what I would have done myself in that location 😅 Envy moment not needed

It's understandable how you feel - I love having kids but occasionally feel nostalgic for my "younger carefree days", although I think I'd feel like that even if I didn't have children as it's partly (for me) just being a bit older.

However I think it's worth considering that what you see as freedom may well be loneliness for your sister and she may envy you (you say she's nervous about her first solo holiday, and that might just be normal nerves but might be her way of telling you she's lonely).

Obviously she might be very happy with her choices - plenty of people are happily childfree, but equally it's possible she isn't childfree by choice.

One of my friends used to tell everyone including her family she didn't want children. 7 years after getting married she announced her pregnancy. Turned out her and her husband had been struggling to conceive.

I fell envious of your sister too! I've been dreaming of a quiet weekend away, just me, a nice little cottage by the sea. One of my colleagues did it earlier this year and she said it was amazing. Sadly, not so easy with a DH who travels a lot for work and a small child!

Every mentally well adult has the life they choose. 100s and 100s of decisions over years have led you to where you are today. So your situation is your choice. If you have serious envy, then that may mean you've made a series of stacked up bad decisions that have led to a place you don't want to be in.

If you are just talking about a minor sense of 'wish I could do that' in the way you might look at Simone Biles tumbling, then everyone has that from time to time because any situation has advantages and disadvantages.

I think it depends…

I’m in your boat and wouldn’t be remotely jealous but I travelled extensively pre kids.

I could be having that life now but i chose children

i do however understand the “wanting a break” or wanting to clock out of your responsibilities. 2 small child can be quite relentless and sleep deprivation doesn’t help….

Perfectly normal case of envy AFAIC! Why wouldn't you be envious?