Crumble added to muffins before baking
If you're asking if the crumble is the source of your problem - it isn't.

Without a recipe and some indication of how you mix and bake your muffins, it is difficult to determine the cause of your cave-ins.  This is a common problem with muffins and cupcakes, though.  The most likely culprits are:  (1) too much liquid in your batter, (2) oven not hot enough, (3) chemical leavener is spent or you used too little, (3) you use too much leavener, (4) you didn't bake them long enough, (5) you used too much batter for each muffin (filling the cups too full), &amp; (6) overmixing.  

If you are following a respected recipe carefully and you know your leavener is fresh, then please make sure you are cooking in an oven that has been pre-heated fully to the temperature in your recipe - that temperature probably shouldn't be below 375°F (and, of course, altitude could be an issue here - how high-up are you?).  Most importantly, mix your ingredients only long enough for them to just barely come together (remember that it's OK if little traces of unincorporated flour are still visible) - mix by hand if you have used an electric mixer in the past.  Finally, avoid filling the cups in your muffin tin more than 2/3 full - using more better doesn't always make larger muffins - at some point, the muffin loses its ability to support the doming of the center.