Recommendation on kids sleeping bag?

I am looking for a sleeping back for my 3 year old son (will be 4 in August).
Mainly for tent camping and camping within a Pop-Up trailer for lower temperatures (lower 20s to 30s).
Something of decent quality but not too pricy since it will not be used that often. Should definetely below $100.
The bag should also prevent him from sliding out in the night. He moves a lot and wiggles himself out of these cheap rectangular sleeping bags.
Unfortunately I cannot find any test reports on kids sleeping bags and therefore I try it here.
I thought about something like this:
http://www.rei.com/online/store/Pro...productId=10218243&parent_category_rn=4500655
http://www.rei.com/online/store/Pro...productId=10218243&parent_category_rn=4500655
http://www.rei.com/online/store/Pro...productId=11435604&parent_category_rn=4500655

Any recommendations?
Thanks a lot for your help
Stefan

I've never used it or know anyone who has. After reviewing the stat's, the Omni Temp Jr. does read like it is perfect for a 4 year old and good to 25 degrees.

Hey Stefan! Welcome to the boards! This is the only one offered here, but it meets your criteria:

http://alpinezone.altrec.com/shop/detail/13065/9

It's for kids up to 5', so your son at 4 years old should get many years out of it. Hope this helps!

EMS used to carry one for people 5' feet or under which might apply to shorter than average women too. the one I bought was rated as a 20 degree bag. (I bought it pre-kids since I was employee getting a discount & we wanted kids, it resides in my 3 years closet for now....)

I bought it in 97 or early 98 & accidently brought it to Europe when my wife & I win July/Early August. We were car camping & I thought I had grabbed a 40 degree bag instead. I ended up sleeping in shorts & a sweatshirt since 1/2 my torso was out of the bag but it was in 40 at night. It rained most of the time we camped so at least the Jr. bag probably some comedy in the tent.

Thanks all for the advice. I start looking around. I have to look at them in the local stores since I have to see and feel them in reality. So far I have focused on the North Face and the Coleman or the house brand form REI. Let's see. I still have some time.
I don't want to by him a high tech one since we don't use it that often but it should be better that the one ("Walmart" type) we currently have.
I myself have a sleeping bag from Ajungilak filled with about 2lbs of goose down. Nice and warm even at very frosty nights. I bought it in Europe a few years ago and really love it. They also make bags for kids but I have never seen them here in the US.

@uphillklimber
We already have one of these. But the temeratures in a popup are not better than in a tent and we spent a couple of days in Colorado last year at freezing temperatures. (It was September and in the upper 20s). And here the "Walmart" bags are just too thin.
My son also moves around in his bed a lot when he sleeps and these kind of blanket type bags have the disadvantage that my son wiggles himself out of it in the night since you can't really close them at the top. So I am looking for something warmer than these cheap bags and something that prevents him from getting out by incident. The mummy shape ones are better for this as I have experienced.

I got both my grandkids 30 and 40 degree bags for people under 5' from campmor or sierra trading post for less than $50 each. I think one is a mummy bag. I mostly car camp with them, so if it's colder, they bundle up in their "warm stuff" (what they call their micofleece clothes) and this year I made them some fleece bag liners. They love them!

My grandgirl and I backpacked last summer and her bag stuffed down good enuff.

They are 3 and 5 now, but I bought the bags when each kid was about 2. Before that, they snuggled with the adults.