Feeling very passed off

Ok so my little girl is 3 and loves lalaloopsy dolls so I told her if she helps clean I will give her money to put away so I put an extra $4 in her money box to night because she has giving up her dummies so I went to count it and found out she is now miss $20 of her money I'm so up set as only person that has been here is my sister how do people think it's right to steal from a child she works hard to earn her money I don't want my child thinking everything you get is for free or want her to be spoilt but I now have no extra money to put in there I feel so up set and the worse mother how could I let this happen 😢 she is going to be so up set now as she was going down town this week to layby a lalaloopsy as there not cheap and she didn't wanna miss out on the special one she wanted