Can You Please Suggest And Help Me To Take The Decision

It is a good news, irrespective of what you finally decide. The school considers her qualified to skip a grade.

Coming to the things to consider when deciding:
- school is placing these kids in 4th grade due to high volume of kids in 3rd grade, not because these kids are being unchallenged in 3rd grade.
- it is happening now, quite a few weeks into the school year. Kid has already formed friendships and is established in the classroom.
- magnet school means academic curriculum is already advanced.
- kid has not expressed that she is bored in the class.

My choice would be to thank the school for the opportunity but have child continue in 3rd grade. There is no real advantage if she moves to 4th grade now. There is no "bragging" rights kind of thing. The curriculum in a magnet school can get challenging in 5th and 6th grades. At that time, being the youngest in class can be a disadvantage. Not just understanding the math, science, language content, but overall interacting with kids who are a year or more older than her. And there is the social aspect -- friendships among girls in elementary school and middle school is a complicated business. There are at least 2-3 heartbreaks that happen over trivial things, to do with cliques and all. Dealing with these at a younger age than others involved can be tough.

Looking further ahead into high school -- the disadvantage of being the youngest in a class gets more pronounced. 11th and 12th grades are quite stressful years. Being younger than needed simply adds to the stress. And even further on, going off to college happens a year earlier.

There is no advantage that I can see if child is not saying she is bored. But, if she is to skip a grade, then now is the time. Doing it later would be harder.