I do not own the impact but a friend of mine got one for one of his sons his older brother got the Omega z5. both are a very good starter & like mentioned the Impact is adjustable. I would start with the load & powder Hunting Man suggested. However remember the Impact only weighs in at 6 1/2 lbs or around that The Omega z5 version is 7 1/2 lbs or around that it will recoil a bit less. I would go to walmart or a gun shop that has both guns let him or her shoulder the guns. If the length of pull on the Omega z5 & weight is not to much I would go with it. The Omega will be a bit more accurate due to not being a break action. Both guns will amaze you tho just get one that fits the shooter right. 70grains of loose blackhorn 209 will do the job out to 100 yards I shoot 90Grains out of my Omega. TC Shockwave 250Grain bullets or Barnes Spit-Fire T-EZ 250Grain would be a good bullet to use as they both come with the hph-24 sabot as supplied seems to be a good fit in TC gun barrels. Pack of regular CCI 209M Magnum shotshell primers & one of them Sabot bullet combos from above with Blackhorn 209 powder load of 70 Grains will be a deadly combo. I started at 80 grains of that powder when sighting in - working up load for best accuracy to me it felt like the recoil of a .410 shotgun with scatter shot or less it was not much. The guns weight eats up lots of recoil & fit helps to. I would not want to load to the max load for Blackhorn 209 of 120 Grains tho I'm sure I would look like this
Hope this helps good luck & happy hunting & good on you for getting the kids out in the woods!