The history of God’s creation (told in Gen. 1—2) tells us that all the land-dwelling creatures were made on Day 6 of Creation Week—the same day God made Adam and Eve. Therefore, it is clear that dinosaurs (being land animals) were made with man.
Also, two of every kind (seven of some) of land animal boarded the Ark. Nothing indicates that any of the land animal kinds were already extinct before the Flood. Besides, the description of “behemoth” in chapter 40 of the Book of Job (Job lived after the Flood) only fits with something like a sauropod dinosaur. The ancestor of “behemoth” must have been on board the Ark.
Juveniles of even the largest land animals do not present a size problem, and, being young, they have their full breeding life ahead of them. Yet most dinosaurs were not very large at all—some were the size of a chicken (although absolutely no relation to birds, as many evolutionists are now saying). Most scientists agree that the average size of a dinosaur is actually the size of a sheep.
For example, God most likely brought Noah two young adult sauropods (e.g., apatosaurs), rather than two full-grown sauropods. The same goes for elephants, giraffes, and other animals that grow to be very large. However, there was adequate room for most fully grown adult animals anyway.
Isaiah 27:1 In that day the Lord with His severe sword, great and strong, Will punish Leviathan the fleeing serpent, Leviathan that twisted serpent; And He will slay the reptile that is in the sea.