I do not think your concerns are unfounded, bunk beds need a safety policy when you have them at home.
We have a bunk bed for our children (two active boys!) have a chance of moving to his own bed/room when he would be ready. If he would be happy to sleep in the regular bed, he would get to sleep in the lower bunk. So the bed was around and standing there unused for quite some while but the 2 year old never happened to be alone in the room and was never really tempted to climb on the lower or higher part of the bunk bed. We've also always been telling the upper bunk is for much older children and we considered to take away (if possible) the attached ladder or the upper bunk if we would be concerned. He had a third under-the-bunk-drawer-bed to sleep on which he also preferred to the bunk for a while. We did hang some kind of a cover on the ladder and stuffed that side with somew pillows to avoid climbing or getting trapped and our little boy did fine in the lower bunk from about age 2,5 I believe, and we added a bed guard on the outer side and stuffing on the wall side for the time being. We always kept on stressing the upper bunk was only for children from age 7 or older and ready to sleep on the upper bed, and that it was NEVER meant to be a place for play or anything else than sleep. Eventually when our youngest passed his fourth birthday he moved to the drawer bed. He is a very active child and sometimes he would climb the upper bunk which he know was not allowed/safe, but we were immediately aware when that happened it would be when he would be in a high energy mood) and he would come off. They both were allowed to try the ladder once in a while with the help of mum or dad, especially going down (I even had to practice again as an adult hıw it worked!) so that by the time one of them WOULD sleep on it, they would be experienced in climbing on and off. The eldest did not want to sleep there untill he was 7 years and the youngest was happy to move to the lower bunk. The eldest sleeps facing the fully enclosed non-ladder side of the bed. There is sufficient light at nighttime to get on andoff. when he's ill he can sleep on the drawer bed. He sometimes forgets to crwal on his knees and stands while getting in but he will learn eventually. When we have other children over and the children go and play in the room, I always accompany them reminding all children present that the upper bed is private territory of my eldest son and for safety reasons only for his sleeping there and so not allowed for play or for anyone to go up there. And, to be honest, when the purchased bed actually stood in our room (actually, initially we wanted it constructed as two seperate beds when the kids would be little, but the workmen did not wish to do this since they knew only how to construct it one particular way, as a bunk), I found it very high above the ground and a bit scary indeed. However, in the first place we did opt for the bunk bed in regard to space-saving and it is really ideal for the long narrow room we have for the children with now space for a desk, cupboards and some play area.
So, I'm really very careful around the bunk bed. But I am also comfortable now about my sons knowing the dangers and the rules. We have few real rules that truly matter at home, so that the children also ralise that the rules that we give most importance too, are about the very serious issue of safety.
Now, if I had the situation of a little one challenging herself (or a parent ;-) to get up there regularly or to sneak in unsupervised, I would also seriously make work of either taking the ladder out/taking the beds apart or preventing her access to the older sibling's room. We used a child safety gate in the children's room's doorway to prevent them going downstairs in the night/dark unsupervised untill a certain age, since a guard rail at the top of the stairs was not possible. Such safety gate could be a way to keep a toddler out, too, while yor older child may be able to open and close it easily by her/himself. Or a special lock on the door could help, or lock the door in daytime when no-one needs to be there untill your little one ages a bit more (2 is a tricky age for discovering...). And provide enough other opportunity to climb and jump elsewhere, foresee a mattress on the floor in a room where you're next to her to use as a trampoline (we did this too), etc. I would personally not be tempted to let a child get accustomed to climbing the bed as fun and play, since it is not for play, but maybe when she's four start to let her learn master the ladder with your help so that she could climb the bed by the time she would use it.
Good luck!
I am telling her "Do not jump, sit, or bounce around on your butt" -- and she is totally ignoring me. I want to encourage her independence and usually am pretty good about NOT being a helicopter mom 
, but it does seem all too easy for her to trip and go flying over the edge. We live in an old house and ds's door does not latch closed, so she can and does push it open very easily. I'm kinda considering having DH disassemble the bed temporarily: the ladder is attached, so the whole bed would have to come down, or I could possibly think of something to put there to block her climbing up unless I am available to supervise. WWYD? Am I being too much of a worry-wort?
