For growing kids, spending 120 on a wetsuit in, IMHO, an extravagance.
Also, for the amount of time they'll spend actually in the water, 3mm neoprene should be OK.
We started off buying 'cheap' wetsuits in Dunnes and/or LIDL. We have also spent a bit more in outdoors shops but never more than 50.
The kids wore them for bodyboarding, sailing and general larking about in the waves. Kids won't be lying on a board in the Atlantic for an hour wating for 'the right wave', so 5mm neoprene is not necessary.