Real bunnies!

Brown or Brown or Brown would be perfect. It's gonna be sooo cute.

I like the top left - as EvelynJo said - if you are going to add flowers and butterflies, then you will get your bright colors there. FYI - when I was 5 I had a stuffed animal names Bunny Blue because indeed, he was blue!

I like the brights it blends better with the quilt.
Bunnys on a quilt can be any color you want them to be

What about some of each? I like them all.

I like the real bunny colours because of the greater contrast. Other coloured bunnies would work too but I would choose darker tones. No matter it will be cute as can be

I don't think the homespuns go with the base fabric as well. And though I prefer the lower left pile, the more natural colors would be good too. Plaid doesn't look like a bunny to me, but small florals are fine. Too bad you can't ask the mom - I like her to be happy when I make a baby quilt, and making what she likes lasts longer than a moment of surprise. Especially if it's a surprise she doesn't like. I made a bed quilt for a daughter years ago, and found out there is an element of it that she does not like, although she loves that I made it. If I'd asked her, it might still be upstairs instead of on a shelf in the basement. Lovely quilt, whatever you do with it.

2 of the bunny colors are nice but I do not care for the darkest one. I personally think that with a bit of bright flowers or foliage will bring the natural color bunnies out and make them really pop however, if I wanted colored bunnies I would make them. All apples are not red if you get my meaning. When a child colors a bunny it is not always a bunny color.

top left is my vote

I would do the colors at top left