Here are the corrected sentences with explanations for the mistakes:

1. **Original:** I play football often on Saturdays.
**Correction:** I often play football on Saturdays.
**Explanation:** The adverb "often" is placed more naturally before the verb "play."

2. **Original:** Do she want to buy a new computer?
**Correction:** Does she want to buy a new computer?
**Explanation:** The auxiliary verb should be "does" instead of "do" because "she" is singular.

3. **Original:** My children doesn't like reading.
**Correction:** My children don't like reading.
**Explanation:** "Children" is plural, so "don't" (do not) should be used instead of "doesn't" (does not).

4. **Original:** We have usually breakfast at six.
**Correction:** We usually have breakfast at six.
**Explanation:** The adverb "usually" should be placed before the verb "have."

5. **Original:** My new shool are in the centre of the town.
**Correction:** My new school is in the centre of the town.
**Explanation:** "School" is singular, so "is" should be used instead of "are." Note: "shool" is corrected to "school."

6. **Original:** Ann usually gets up at 6 o'clock and have breakfast at 6.30.
**Correction:** Ann usually gets up at 6 o'clock and has breakfast at 6.30.
**Explanation:** The subject "Ann" is singular, so "has" should be used instead of "have."

7. **Original:** You don't see often this bird in daytime.
**Correction:** You don't often see this bird in the daytime.
**Explanation:** The adverb "often" is better placed between "don't" and "see." Also, "the daytime" is the more appropriate phrasing.

Here are the corrected sentences:

1. I often play football on Saturdays.
2. Does she want to buy a new computer?
3. My children don't like reading.
4. We usually have breakfast at six.
5. My new school is in the centre of the town.
6. Ann usually gets up at 6 o'clock and has breakfast at 6.30.
7. You don't often see this bird in the daytime.