I would ask the mom if they want new quilts. If she says yes, get her to measure the size she wants including drops. I have found that shams work the best with kids. You never know. If they say no, that's okay. You didn't spend time making something that doesn't work for them.

Kids from a very young age are given snuggly manmade fiber blankets. Personally, I'm not a fan - but it's what they are exposed to and they quickly become a favorite. Think minky or fleece.

Quilts are also harder to care for. Those same blankets mentioned above go into the washer and dryer, no special handling required. They aren't as bulky and dry quickly.

I love the weight of quilts with cotton batting, and only use natural fibers - but that is not what most younger people want. I like Sewingitalltogether and WesternWilson's suggestions.

My mom has a bunk bed at their 'beach house'. It is really difficult to make. Someone has to crawl up there and try and 'tuck' it in around the mattress which is really snug up against the frame without bashing your head on the ceiling! Ooof. It definitely doesn't go 'under' the mattress. I was happy when the 'kid' was old enough to help out!! I like the idea of a 6-7 drop on the sides and perhaps even that on the end. Maybe you should ask if the mattress is a standard size? (My mom has a purchased blanket from Tuesday morning.)

My two sons had bunk beds and never made their beds so I just had a small blanket on each bed just so they could keep warm. It is very hard to make the beds on a bunk bed. Good luck to you and I am sure you will get some wonderful advice on this subject

Maybe mom is the one you should be consulting on what look she'd like, if the girls are that young!

Peaceandjoy raises some great issues. I like wool batting for everything...nice drape, warm but light. And I love flannel backing for quilts as well, everyone loves that softness. The other option is backing with a gauze-like fabric that washes up very soft.

Personally I loathe minky and fleece as backings. And I refuse to make anything I loathe!

Our bunkbeds for grandsons are up against a wall and are not easy to make neat. One must step on ladder to make top bunk, and reach over around safety rail ( if there's one), and on bottom bunk, reaching in without banging your head is a challenge! My solution would be to make it easy on mom and safe for kids to make bed. One side should have a " drop " of 8 to 10" ( top one can be tucked while bottom one hangs loose. The rest should just cover the 48x 72" surface. A little ( 8") longer may be ok if end of bed is visible and will need tucking. So l suggest 58 x 72 to 80".

I made a quilt that is just as wide as the mattress and about 12-15inches shorter. The bunk beds have low tog duvets with plain white duvet covers. The quilts just lay on the top.

Bunkbeds are one issue. Quilts for family members is another. I'm coming to terms with my small-footprint son and family just don't need and probably don't really want many more quilts from me right now. I still get to keep stuff at grandma's house though!

So for actual bunk beds placed up against a wall, you need to go for a size that maybe isn't the nicest to wrap up in -- except they are great for slightly large couch cuddles! Keep the width narrow, like 60" or under and the length long so it can be tucked in firmly at the feet with the sides basically too short to tuck well. Whether that goes up to pillow line, or further, is up to you, but add about 12" for the tuck.

And then there is the possibility of the bunks being separated in which case you basically just want twin quilts. I didn't get the fabrics collected in time for my own son's bunkbeds but maybe for my grandson. Or maybe he can have one at his house and one at grandma's. Or maybe it will be clear it is time to go to someone else.
https://www.quiltingboard.com/member...14-621640.html