We got this suit for our 4 1/2 year old son (whose crazy about space) for Halloween.  It's seems well made (has already made it through the wash) and he loves wearing it.  It's lightweight with lots of snaps.  The size 4/6 seemed to fit him well over jeans/shirt so maybe go up a size if your child is at the size 6 range.

We also got the boots&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Astronaut-Boots-size-Medium/dp/B0015MDVTO/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Astronaut Boots, size Medium</a>, gloves (which match) and the plastic space helmet.  Boots were fun and had reflectors on them (nice for trick or treating).  The gloves were a little bulky and so he didn't enjoy wearing them as much.  The space helmet&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Jr-Astronaut-Helmet-with-sounds/dp/B0008F6WMM/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Jr. Astronaut Helmet with sounds</a>&nbsp;broke almost instantaneously.  It has a major design flaw in that you can only lift up the visor using a button.  So you can imagine how long that lasted with a 4 year old.  It was also extremely large (fits comfortably on adults).  So all in all, for a 4 year old, I'd definitely get the suit, probably the boots, would skip the gloves and would try some other helmet for your junior astronauts in training!