Parents who don't watch their kids

Gracie • Mother of two, military spouse, aspiring nurse 💉
So I took my two daughters to the park last night. I go to put my youngest who's 7 months old in the swing for the first time and some little girl comes up to my stuff that is beside me and grabs my oldest daughters scooter. So I put my hand on the scooter and I said I'm sorry but you can't play with this toy. And she wouldn't let go. So I tried to ignore it and get back to putting my daughter in swing.Well the little girl then tried to scoot away with it. I go back and say where are your parents. This isn't your toy this is hers pointing to mt oldest and I said I'm sorry but you can't play with this. Well the girl wouldn't tell me where her parents were so I asked her again will you please let go and she ignored me. So then I started asking people around me if they knew who her parents were. Her parents were nowhere to be found. So I asked her again to take her hands off and guess what she didn't do it So I peeled her hands off and she was like don't touch me! I said well don't touch things that aren't yours. And took the scooter. The little girl walked away and played with another girl. I played with my daughters and waited for that girls mom to come up.  Her mom came back 30 min later while it was getting pitch black out. I stopped her and told her what her daughter did and do you know what her mom said. Well she's only 3 I said I don't care how old she is, she should know better and as a mom I thought you should know because as a mom myself I would want to know. And she told me that well she's just so little and doesn't know better she's just 3 and I was like well as parent I thought you should know.  And left.
My kids knew early on way way before 3 what the word no means. 
Has anyone else dealt with another kid touching your things without permission at the park? How did you handle the situation?. I was just in shock of her daughters attitude. 
Btw the park is huge ( recreation) . 3 playgrounds, swing area, basketball courts, baseball field.