Move up to booster or stay in 5 point harness - Canada

I have 2 evenflo 5 point harness car seats that were manufactured in 2005/2006
Both purchased brand new for my now 9 yr old and 11 yr old. Great shape, no accidents and well taken care of (no twisted straps etc)
I have a 43 lbs 4 yr old and 39 lbs 3 yr old currently using these seats.
I had originally planned to keep my 2 littles in the 5 point harness to the max weight of 50 lbs (per manufacturers instructions). However, now I am considering purchasing 2 new boosters.
My question is should i purchase new boosters or continue with expired 5 point harnesses for another short while?
Also please tell me what booster to buy ... High back, low back. I am on information over load
Thanks so much

Re: Move up to booster or stay in 5 point harness

Well, you kinda have a few items to address. Going a couple of months over the expiration isn't a big deal in a well maintained seat, but these seats are 2-3 years expired so your kinda past that point already.

One of the things I like to ask parents when they are debating between a booster or a harness is: if your child is playing with a ball and it rolls into the street, would they run after it impulsively, or would they stop and look both ways without being reminded. The brain processes for remembering street safety even when distracted by a missing toy, are the same brain processes that will keep a kid from unbuckling to get the toy they just dropped on the floorboard, or leaning out of the shoulder belt to whack that annoying sibling.

If your 4 year old is very mature and calm, you may be ok with a booster, but I'd suggest a high back, especially if car rides are still sleep inducing. I'd want to do a trial run with a borrowed booster (preferable on a bad day so you can get a feel for what happens when kiddo is too cranky/tired/four to cooperate) to make sure you don't actually need a harness since most kids don't do well with full time booster use until 5-6 years old. My own kids were not ready for full time boosters at 4, but I did start training them gradually at that age by letting them ride in a booster for short fun trips where they wouldn't fall asleep and were motivated to be good.

A harness seat would be best for your 3yo. If you let us know what kind of budget you have for seats, what car they will be going in, and seated shoulder height, we can help you pick out some seats.

I would buy each child new seats as soon as possible.

I would purchase 5 point harnessed seats, not boosters. The 3 year old is both too lightweight and too young for a booster. The 4 year old weighs enough, legally, but is on the young side.

Evenflo Maestro seats should work really nicely.

I'm guessing you have Evenflo Express/Visions/Traditions seats currently, and those have 16 inch top harness slots. As soon as a child's shoulders are level with those top slots the 5 point harness is outgrown. No guarantee you make it to the max harnessing limit, which I'm guessing is 47 pounds.

The Maestro offers 18 inch top harness slots. Nice and high, and with a 50 pound harnessing max. Also later converts to a decent highback booster.

The Maestro is on rollback at Walmart.ca right now for $90. I assume it's the same price in-store as well.
http://www.walmart.ca/en/ip/evenflo-maestro-combination-booster-wesley/6000069431950