Flower Girl and Ring Bearer Outfits

Personally I think this depends. I think it’s fine to have the parents pay for it if you’re open to finding something that works within their budget. If you have a specific outfit in mind that they might not be comfortable spending that amount on, you should pay for it.

I think the Bride and Groom should pay for them. But there isn't a cut and dry rule

I found their outfits at really good prices, one FG is my youngest sister (she is 7) so my mom is buying her dress (50 on Etsy). My other FG is my FH's neice, and his nephew is RB, and their mom (FH's sister) said she will be paying for them as well.

I will be paying for our flower girl and ring barrer outfits. They will probably never wear them after the wedding so I didn't want the parents paying for the specific outfit to only wear once. I'm only spending $100 altogether for both outfits so I didn't think it was that big a deal.

It depends. I let my aunts choose the outfits for their kids. I didn't care what they wore. They chose dresses on Amazon for 20 dollars each that were great! The boys outfits came from target. They just wore a nice pair of shorts and a white button down. I bought their bowties/suspenders. I also let them choose their shoes. I paid for the flower girls hair. Then I got them all gifts.

I paid for my flower girls crowns but not the dresses or sash. The dress is reasonable @ $40 & I told their parents for them to wear any whitish shoes that they have & fit into. They are both 3x & will grow out of any shoes really fast.
I paid for the junior groomsmen suits (mainly bc I got them from Kohl’s & w/ the Kohl’s card, Kohl’s cash from a previous purchase, and Kohl’s elite shopper I got such a great deal - like $35 per each). The parents tried to pay me back, but I told them no, just buy the suspenders & bow ties. The dress pants also needs to be hemmed for 2x of the boys. But their mom is handling as they are charcoal gray & will also serve double duty as their Christmas outfits. They are responsible for the belts, shoes & socks.
I don’t think that there’s any cut & dry rule. Just talk to the moms (&/or dad’s).

At first when I asked the parents if their child wanted to be a RB/FG I didn't say anything about the outfits. Later after we budgeted more and found out FH's tux wasn't going to cost as much we offered to pay for their outfits. FG dress is only $40 with a $13 sash. RB toddler tux is only $50-70.

That really needs to be a discussion between the couple and the child's parents. One of my bridesmaids is also my flower girl's mom. On top of her own dress, and being a single mom, I didn't want her to feel like she needed something spectacular for her daughter. I said anything all white will be fine, I didn't care where it came from . A trip to Ross and $10 later, she found a dress! In return I got her a very nice flower crown to complete the outfit.