jumping up and down in crib (on knees)

One of my girls is very good at self-soothing - she sucks her thumb (other one doesn't) and lately she has been holding on to the sides of the crib and manically jumping up and down on her knees. She went through a phase abut 8 months ago when she got on hands and knees and rocked herself to sleep (apparently DH did that, so maybe it runs in the family!)
Now, every time she goes down for a nap and at night, she will jump up and down for several minutes while I am still in the room and after I have left until she lays herself down to go to sleep. I am a little afraid that the bed might break (!) because she is pretty wild (she does it smiling, so she clearly loves doing it!) but I am more concerned that she has woken up at 3AM about 4 times in the last 2-3 weeks and jumped up and down like this for 30-40 minutes before going back to sleep. She doesn't wake her twin, and she doesn't cry, so we haven't gone in. Obviously, she is very tired the next morning!
Is it just a phase? Should I go in and try to make her lie down again? Has anyone heard of this?

 

Both of my girls will jump up and down in the bed constantly. They will actually jump up and fall down on their butts like it's a trampoline--over, and over, and over. They sometimes do this the entire time they should be taking a nap. Now, I don't recall them waking up in the middle of the night and jumping, but they have been jumping for months now, maybe even a year, and so far our beds have held up and ours are secondhand. It just sounds to me like she is enjoying a bouncy crib. I've tried to stop mine, but it doesn't work, as soon as I leave the room it's back to bouncing.

 

She is absolutely enjoying her bouncy crib! The other one will join in sometimes, they look like little jumping beans, cackling at each other, but she woke up at 3:45 again last night and I heard her jumping. It is almost exactly 9 hours after we put them to bed (6:30 pm), so I would say maybe she only needs 9 hours of sleep? But she is my "tired one" and would still take 2 naps a day if her sister allowed it. She is always ready to have a nap at 10:30 am, so I don't know...

 

Sounds to me like she discovered a new trick and is willing to try it at anytime. One of my boys wakes on occasion at about 4am and he just talks and talks like he does during the day. It must be just about when they are coming out of a state of total sleep and their bodies are slowly starting to wake up and they decide to just hang out for a bit.

 

She's found a built in toy!!! My girls are still in their cribs and are pretty big for their age (they'll be 3 on Monday and Natalie is 43lbs and Brooke is 36lbs, they are 41inches tall). They've been jumping since they figured out how to stand and our cribs have stood up to all the fun. I always thought that they were jumping while standing, but one day I walked in when Natalie was doing it and she was doing it on her knees too! Natalie also does it when she's having one of her "parties" during the night too. So I don't think its anything to worry about.

Happy jumping!!

 

Both of mine jump. I can hear it through the baby monitor -- that's how I know they're awake. I really never thought much of it. I think it's pretty normal.