Using a panel or large print fabric is my suggestion. What they like at 2 and 4 is not what they will like in a few years. My suggestion is to make it simple and bright so that they love it now. Have fun.

Dinosaur Patterns - Popular Dinosaur Quilt Patterns You Need (freeapplique.com)
Here is another site for free dinosaurs applique patterns. Children are attracted to bright colors to stimulate their minds. How about something simple like a nine patch block with a couple of dinosaurs appliqued in various spots. Don't stress about it. I'm sure you can get some great idea's from Pinterest. Just search for children's dinosaurs quilts.

Keep it simple. Dino fabrics in bright happy colors. I find that kids like to wrap themselves up in quilts. Large enough for them but not necessary to do a bed size. Minky or soft back is a favorite. Make them the same but different. Siblings fight over anything each one needs to be easily recognizable as to who it belongs too. Like a blue border or a red border.

I wouldn't spend a lot of time or money on the quilts, because of their ages they wouldn't know about the time and money that goes into making a quilt. Use your stash or maybe a panel and using your stash to make it the size needed.

I sew play quilts for my grands all the time. I use panels. Their favorite theme changes and of course they need a new quilt with that theme. They love all their quilts, except the baby theme ones. LOL

I also would find dinosaur panels and add borders. I have done that and little boys (especially) really like that. When I made one for a grandson I used a panel, a very thin border and another border of squares. Turned out good I thought.

Lizzie3 ... OMG how did I miss this, and with you being a fellow Canuck .........
Being that the kids like dinos, they no doubt want and need a Toronto Raptors quilt!
Surely, you could oblige them!!!! :)

I am with the others. I would not make a bed sized quilt for boys those ages. I would not put a lot of time or work into them either. I made a Grandson an appliqued dino quilt when he was young. He never got to use it. He is now 33 and not interested in it.

I am sure the quilts will be washed often. Did she say what size the beds are? That would be important to know. I would not make anything really taking too much time as the kids will use the quilts for a few years maybe. However, they may keep them to use on the couch or whatever. I would say just get some dinosaur fabric , just prints or panels, add a few bright borders and call it good.
I just went to Handcock's of paduka and entered "dinosaur" into the search and got a lot of different ones. I sure that a lot of quilt shops will have a search feature .

I did a quilt with dinosaur themes for a child awhile ago - I found a dinosaur silhouette (from a colour page free on line) and used Golden Threads paper to stitch that shape in several places. I think the bright colours are a must, and if you can include some dinosaur fabric I think that would make it even better!