Do these constructions mean the same ?
I used to play football when I was a child.
I was used to play football when I was a child.
And
I got used to play football.
Not quite. Assuming you mean that "At some point in the past I played football", of your three sentences "I used to play football" is the only correct one in this case. And to clarify, "I used to play football" implies that you did play it in the past but you do not play it now.
"I was used to play football" suggests passive voice, so unless you were the football it's probably not what you mean.
Typically "got used to" means "became accustomed to". However it also takes a present participle in the verb following, so if you want to say that you became accustomed to football you would say "got used to playing football", but that also doesn't quite mean the same as what you intend.
I used to play football when I was a child.
You would play football when you were a child. You probably don't play it anymore. The grammar rule is "used to, didn’t use to".
I was used to playing football when I was a child.
In the past, you were accustomed to the activity. Playing football was your usual thing. The expression is "be used to".
I got used to playing football.
At present, you have become familiar with playing this sport. The expression is "get used to".
Notice the gerund in these two sentences.
They mean slightly different things:
In this context it means that the speaker played football as a child, but doesn't any longer.
(Note that is is the present tense "playing" rather than "play" from your example.)
The phrase "was used to"/"is used to"/"getting used to" refers to becoming accustomed to an environment, requirement, knowledge or events.
For example, "After a few days, John's new cat was getting used to their new surroundings", or "I don't know how to use public transport any more, but when I was young I was used to getting the bus", or "He didn't like the taste of the food here, but he ate it anyway. He was used to it by now."
The phrase "I was used to playing football when I was a child" means that the speaker often played football when they were a child.
This is just a different tense but with similar meaning to the above.
"I got used to playing football" = "I became accustomed to playing football" (This implies the speaker had not played football, but then started playing and adjusted to playing it regularly.)
"I was used to playing football" = "I was accustomed to playing football" (This implies the speaker regularly played football, and was accustomed to playing it regularly.)