Past habit

Hi, I would like to ask you about expressing a habit in the past. I know that we use the past simple, used to or would to express a past habit. However, there are some verbs which I would not use in the past simple to express this meaning, e.g. buy...It is said that the past simple is used for completed actions, so I assume when I say I bought a lot of sweets, it means that I paid for them and I already have them. So in the sentence When I was a child, I bought a lot of sweets it seems to me that it is incorrect to use bought for repeated action or habit, because it seems like a single action. I know that the given sentence talks about a past habit. However, does it not express a completed action?

I would say I bought a car yesterday. I bought these apples twice. However, when I want to express a process of byuing, I would say When I was a child I was byuing a lot of sweets to express repeated activity. Am I right or should I use the past simple?

I would be very glad if you could help me.